VMware: Optional create backing parameters

The current create backing methods do not support specifying an adapter
type for the backing VM. These methods always create a backing VM with
a single disk and LSI logic adapter. This change adds optional parameters
to create backing methods so that a backing VM can be created without a
disk or with a specific adapter type.

Partial-Bug: #1284284
Partial-Bug: #1287185
Partial-Bug: #1287176
Change-Id: Ifff64eb2be4af1c4218e810366e25dbecdc5847f
Merge "VMware: Optional create backing parameters"