Added vcenter support for ostf tests.

Because in the configuration with vCenter compute node is missing, added:
1. Getting type of virtualization from cluster settings
2. Processing case when the type of virtualization is vmvare (not checked for no compute node available)
3. In test_sanity_infrastructure compute node has been replaced by a controller because
   for vmvare and neutron interaction occurs via controller node

Implements: blueprint vcenter-hv-full-scale-support
Change-Id: I4f74011de5548990f163f220632fbf4fe2ffa39e