Added supports_snapshots? method to base/sub class.

- Added supports_snapshots? method to base  class that returns false and added supports_snapshots? to VmVmware subclass to return true as that allows snapshot functionality for VM .
- Updated hover text for buttons to show 'Revert' in the hover text for Revert button instead of 'Remove', and changed word 'Operations' to be lowercase in the hover text message.

https://bugzilla.redhat.com/show_bug.cgi?id=1141174
https://bugzilla.redhat.com/show_bug.cgi?id=1141375