VMware: Resize operation fails to change disk size

The finish_migration step will resize the cpu and memory to match
the new flavor chosen, but not the disk size. Additional code was
added to extend the disk size using ExtendVirtualDisk_Task.

DocImpact

Change-Id: Iff10443f603d329d01a74a620079f80518b75a50
Closes-bug: #1291741
Merge "VMware: Resize operation fails to change disk size"