[Core][BugFix] Fix docker runtime env on Azure

[cblmemo]

This is a bug introduced by #3362 , where the code assume image_id is always of format <publisher>:<offer>:<sku>:<version> but ignore the case of docker image as runtime environment.

To reproduce:

$ sky launch --cloud azure --image-id docker:ubuntu:20.04
I 04-18 18:55:57 optimizer.py:693] == Optimizer ==
I 04-18 18:55:57 optimizer.py:704] Target: minimizing cost
I 04-18 18:55:57 optimizer.py:716] Estimated cost: $0.4 / hour
I 04-18 18:55:57 optimizer.py:716] 
I 04-18 18:55:57 optimizer.py:839] Considered resources (1 node):
I 04-18 18:55:57 optimizer.py:909] ----------------------------------------------------------------------------------------------
I 04-18 18:55:57 optimizer.py:909]  CLOUD   INSTANCE          vCPUs   Mem(GB)   ACCELERATORS   REGION/ZONE   COST ($)   CHOSEN   
I 04-18 18:55:57 optimizer.py:909] ----------------------------------------------------------------------------------------------
I 04-18 18:55:57 optimizer.py:909]  Azure   Standard_D8s_v5   8       32        -              eastus        0.38          ✔     
I 04-18 18:55:57 optimizer.py:909] ----------------------------------------------------------------------------------------------
I 04-18 18:55:57 optimizer.py:909] 
Launching a new cluster 'sky-32ec-txia'. Proceed? [Y/n]: 
I 04-18 18:55:59 cloud_vm_ray_backend.py:4226] Creating a new cluster: 'sky-32ec-txia' [1x Azure(Standard_D8s_v5, image_id={'eastus': 'docker:ubuntu:20.04'})].
I 04-18 18:55:59 cloud_vm_ray_backend.py:4226] Tip: to reuse an existing cluster, specify --cluster (-c). Run `sky status` to see existing clusters.
I 04-18 18:56:00 cloud_vm_ray_backend.py:1363] To view detailed progress: tail -n100 -f /home/txia/sky_logs/sky-2024-04-18-18-55-56-923553/provision.log
Clusters
NAME                          LAUNCHED     RESOURCES                                                                  STATUS   AUTOSTOP  COMMAND                       
az-test-2                     10 hrs ago   1x Azure(Standard_NC4as_T4_v3, {'T4': 1}, image_id={'eastus': 'docker:...  STOPPED  -         sky exec az-test-2 nvidia...  
doc-debug-new                 3 weeks ago  1x GCP(g2-standard-4, {'L4': 1})                                           STOPPED  -         sky start doc-debug-new       
sky-spot-controller-4a0782e9  4 weeks ago  1x AWS(m6i.2xlarge, disk_size=50)                                          STOPPED  10m       sky spot launch -n t-spot...  

Traceback (most recent call last):
  File "/home/txia/miniconda3/envs/skyserve/bin/sky", line 8, in <module>
    sys.exit(cli())
  File "/home/txia/miniconda3/envs/skyserve/lib/python3.9/site-packages/click/core.py", line 1157, in __call__
    return self.main(*args, **kwargs)
  File "/home/txia/miniconda3/envs/skyserve/lib/python3.9/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
  File "/home/txia/skypilot/sky/utils/common_utils.py", line 354, in _record
    return f(*args, **kwargs)
  File "/home/txia/skypilot/sky/cli.py", line 805, in invoke
    return super().invoke(ctx)
  File "/home/txia/miniconda3/envs/skyserve/lib/python3.9/site-packages/click/core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/home/txia/miniconda3/envs/skyserve/lib/python3.9/site-packages/click/core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/home/txia/miniconda3/envs/skyserve/lib/python3.9/site-packages/click/core.py", line 783, in invoke
    return __callback(*args, **kwargs)
  File "/home/txia/skypilot/sky/utils/common_utils.py", line 375, in _record
    return f(*args, **kwargs)
  File "/home/txia/skypilot/sky/cli.py", line 1069, in launch
    _launch_with_confirm(task,
  File "/home/txia/skypilot/sky/cli.py", line 597, in _launch_with_confirm
    sky.launch(
  File "/home/txia/skypilot/sky/utils/common_utils.py", line 375, in _record
    return f(*args, **kwargs)
  File "/home/txia/skypilot/sky/utils/common_utils.py", line 375, in _record
    return f(*args, **kwargs)
  File "/home/txia/skypilot/sky/execution.py", line 452, in launch
    return _execute(
  File "/home/txia/skypilot/sky/execution.py", line 267, in _execute
    handle = backend.provision(task,
  File "/home/txia/skypilot/sky/utils/common_utils.py", line 375, in _record
    return f(*args, **kwargs)
  File "/home/txia/skypilot/sky/utils/common_utils.py", line 354, in _record
    return f(*args, **kwargs)
  File "/home/txia/skypilot/sky/backends/backend.py", line 57, in provision
    return self._provision(task, to_provision, dryrun, stream_logs,
  File "/home/txia/skypilot/sky/backends/cloud_vm_ray_backend.py", line 2668, in _provision
    config_dict = retry_provisioner.provision_with_retries(
  File "/home/txia/skypilot/sky/utils/common_utils.py", line 375, in _record
    return f(*args, **kwargs)
  File "/home/txia/skypilot/sky/backends/cloud_vm_ray_backend.py", line 1990, in provision_with_retries
    config_dict = self._retry_zones(
  File "/home/txia/skypilot/sky/backends/cloud_vm_ray_backend.py", line 1437, in _retry_zones
    config_dict = backend_utils.write_cluster_config(
  File "/home/txia/skypilot/sky/utils/common_utils.py", line 375, in _record
    return f(*args, **kwargs)
  File "/home/txia/skypilot/sky/backends/backend_utils.py", line 789, in write_cluster_config
    resources_vars = to_provision.make_deploy_variables(cluster_name_on_cloud,
  File "/home/txia/skypilot/sky/resources.py", line 951, in make_deploy_variables
    cloud_specific_variables = self.cloud.make_deploy_resources_variables(
  File "/home/txia/skypilot/sky/clouds/azure.py", line 313, in make_deploy_resources_variables
    publisher, offer, sku, version = image_id.split(':')
ValueError: not enough values to unpack (expected 4, got 3)

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
  • The reproducible code above
• All smoke tests: pytest tests/test_smoke.py
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
• Backward compatibility tests: bash tests/backward_comaptibility_tests.sh