In VolumeSnapshotContent, if the CSI driver does not match the plugin's,
the controller should skip this content instead of always processing it.
This PR also add a few tests related to snapshot and content static
binding.
During binding, if content specify its bound snapshot uid and it
does not match the snapshot's uid, the content object and also the
physical snapshot will be deleted. In this case, the controller will
treat the content as an orphan content because its snapshot object does
not exist (deleted) any more.
