Add unit tests

[abrarshivani]

Add unit tests so that issues can be captured in make ci

[luomiao]

Unit tests should be added for new vSphere functionalities/tasks/code.
Usually the unit tests simply reside together with the code need to be tested.
For example,
https://github.com/kubernetes/kops/blob/master/upup/pkg/fi/cloudup/awsup/aws_utils.go
has its corresponding tests at:
https://github.com/kubernetes/kops/blob/master/upup/pkg/fi/cloudup/awsup/aws_utils_test.go

Similarly, vSphere's utility code at:
https://github.com/kubernetes/kops/blob/master/upup/pkg/fi/cloudup/vsphere/vsphere_utils.go
may have its tests vsphere_utils_test.go at the same folder.

Guideline for unit tests:
(I am just borrowing from kubernetes' unit tests guide)

• Unit tests should be fully hermetic
  • Only access resources in the test binary.
• All packages and any significant files require unit tests.
• The preferred method of testing multiple scenarios or input is table driven testing
  • Example: TestNamespaceAuthorization
• Unit tests must pass on OS X and Windows platforms.
  • Tests using linux-specific features must be skipped or compiled out.
  • Skipped is better, compiled out is required when it won't compile.
• Concurrent unit test runs must pass.
• See coding conventions.

We may not need unit tests for every file at once. But we should have the unit tests for significant files first.
Current vSphere packages and files:
pkg/model/vspheremodel/
pkg/resources/delete_cluster_vsphere.go
protokube/pkg/protokube/vsphere_volume.go
upup/pkg/fi/cloudup/vsphere/
upup/pkg/fi/cloudup/vspheretasks/

[pdhamdhere]

@casualjim We need to put framework in place to easily add and run these unit tests.

[fabulous-gopher]

This issue was moved to kubernetes#2745