Revert "mark oslo.vmware as optional dependency"

Revert "mark oslo.vmware as optional dependency"

This reverts commit e67adc385ce6997249fbf70e9402264f758fc6f4.

Adding optional dependency tracking would be nice,
but Cinder is not yet in a place to do this.

- Cinder supports tox 1.6 (minversion in tox.ini)
- This functionality does not work on 1.6, requires 1.7.  Tox
  fails to build a test environment if using tox 1.6.
- We have decided we can't move to tox 1.7 for now.
  ( https://review.openstack.org/#/c/211614/ )

This reverts commit 478e8e970e54aaf3a034dc6347605c1b18291d0d.
- Need to remove oslo.vmware from test-requirements.txt now, as
well.

Closes-Bug: #1484035

Change-Id: Icff52508ff1cd67e8c17964c840d3a5cdcfbbce3