VMware: spawn refactor - DatastorePath class

Part of spawn refactor work to consolidate a lot of the datastore path
manipulation code. The DatastorePath class is a simpler version of a
class of the same name in earlier versions of
https://review.openstack.org/#/c/87002, and is intentionally limited in
the ways that DatastorePath objects can be constructed. No attempts are
made to ensure that the datastore, directories and files referenced in
these objects are valid on the remote system.

partial blueprint vmware-spawn-refactor

Change-Id: Id65d0308d32835048229e7a3d98b84af2b13583c
VMware: remove dsutil.split_datastore_path

The functionality of split_datatore_path has been subsumed by
the DatastorePath utility class, so remove it and convert
all callers to use the latter.

Change-Id: I07a2cfe15fccaca4aee25bc43157e6c604b91831
VMware: spawn refactor - Datastore class

Introduces the start of a simple Datastore class to encapsulate relevant
data of a datastore.

partial blueprint vmware-spawn-refactor

Change-Id: Ic0ee6cdd47e7cbd66cf456776c61d0b85fb51a0a
Merge "VMware: spawn refactor - DatastorePath class"
Merge "VMware: remove dsutil.split_datastore_path"
Merge "VMware: spawn refactor - Datastore class"