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Add vSphere Cloud Provider simulator based tests

**What this PR does / why we need it**:

Initial set of vSphere Cloud Provider functional tests against the vCenter simulator, provides test coverage without having to run against a real vCenter instance.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

The vsphere simulator recently moved from vmware/vic to govmomi, I had discussed the idea of introducing it for testing with vSphere Cloud Provider maintainers.  These tests provide 90%+ coverage for vclib/datacenter.go, but we can expand further of course.

**Release note**:

```release-note
NONE
```