Azure blob storage support

[pmcatominey]

Adds a Detector and getter for Azure Blob Storage with dependencies on:
github.com/Azure/go-autorest/autorest/azure
github.com/Azure/azure-storage-go

Fixes #33.

An access key is required for the SDK Client, public blobs should be able to
make use of the http Getter anyway.

Tests passed against a storage account on my own subscription, as far as setting an account up for this the requirements are in get_azure_blob_test.go. I'm not sure how the access key would be kept safe however.

go test -v -run "TestAzure"
=== RUN   TestAzureBlobDetector
--- PASS: TestAzureBlobDetector (0.00s)
=== RUN   TestAzureBlob_impl
--- PASS: TestAzureBlob_impl (0.00s)
=== RUN   TestAzureBlobGetter
--- PASS: TestAzureBlobGetter (3.56s)
=== RUN   TestAzureBlobGetter_subdir
--- PASS: TestAzureBlobGetter_subdir (0.92s)
=== RUN   TestAzureBlobGetter_GetFile
--- PASS: TestAzureBlobGetter_GetFile (0.09s)
=== RUN   TestAzureBlobGetter_GetFile_badParams
--- PASS: TestAzureBlobGetter_GetFile_badParams (0.00s)
=== RUN   TestAzureBlobGetter_GetFile_notfound
--- PASS: TestAzureBlobGetter_GetFile_notfound (0.08s)
=== RUN   TestAzureBlobGetter_ClientMode_dir
--- PASS: TestAzureBlobGetter_ClientMode_dir (0.08s)
=== RUN   TestAzureBlobGetter_ClientMode_file
--- PASS: TestAzureBlobGetter_ClientMode_file (21.87s)
=== RUN   TestAzureBlobGetter_ClientMode_notfound
--- PASS: TestAzureBlobGetter_ClientMode_notfound (0.10s)
=== RUN   TestAzureBlobGetter_ClientMode_collision
--- PASS: TestAzureBlobGetter_ClientMode_collision (0.10s)
PASS
ok  	github.com/hashicorp/go-getter	26.814s

[kraihn]

@pmcatominey, are you still working on getting this through? If not, I'd be interested in helping get it done.

[pmcatominey]

@kraihn I am not, if you want to take the branch, let me know and I'll close this PR!