Add first e2e test case

[leakingtapan]

What is this PR about? / Why do we need it?
Assuming a cluster is created and CSI driver is deployed, this test case automates the steps:

1. create storageclass, pvc
2. create pod
3. make sure the pod is running (this means the volume is mounted
   successfully)

What testing is done?
Added a test script ./hack/run-e2e-test

>> ./hack/run-e2e-test

=== RUN   TestE2E
Running Suite: AWS EBS CSI Driver End-to-End Tests
==================================================
Random Seed: 1543987438
Will run 1 of 1 specs

Dynamic Provisioning
  should create a volume on demand
  /Users/chengpan/workspace/csi-ebs/src/github.com/kubernetes-sigs/aws-ebs-csi-driver/tests/e2e/dynamic_provisioning_test.go:35
Creating StorageClass: testdata/dynamic_provisioning/storageclass.yaml
Creating PVC: testdata/dynamic_provisioning/claim.yaml
Creating Pod: testdata/dynamic_provisioning/pod.yaml
Pod is running
Deleting Pod: testdata/dynamic_provisioning/pod.yaml
Deleting PVC: testdata/dynamic_provisioning/claim.yaml
Deleting StorageClass: testdata/dynamic_provisioning/storageclass.yaml

• [SLOW TEST:37.039 seconds]
Dynamic Provisioning
/Users/chengpan/workspace/csi-ebs/src/github.com/kubernetes-sigs/aws-ebs-csi-driver/tests/e2e/dynamic_provisioning_test.go:33
  should create a volume on demand
  /Users/chengpan/workspace/csi-ebs/src/github.com/kubernetes-sigs/aws-ebs-csi-driver/tests/e2e/dynamic_provisioning_test.go:35
------------------------------

Ran 1 of 1 Specs in 37.039 seconds
SUCCESS! -- 1 Passed | 0 Failed | 0 Pending | 0 Skipped
--- PASS: TestE2E (37.04s)
PASS

[k8s-ci-robot]

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This pull-request has been approved by: leakingtapan

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[coveralls]

Pull Request Test Coverage Report for Build 215

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 51.035%

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Totals
Change from base Build 210:	0.0%
Covered Lines:	567
Relevant Lines:	1111

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💛 - Coveralls