vSphere hypervisor plugin

Convert vSphere hypervisor configuration in Nova to the new plugin setup.

Change-Id: Ibf6f5918e6a8d8a7b7784dac832d806e993cff8f
Merge branch 'config-local' into dt-test
Merge branch 'hypervisor-xenserver' into dt-test
Merge branch 'hypervisor-vsphere' into dt-test