VMware: Fixes the instance resize problem

The fix includes separating out methods for
associating/disassociating a vsphere vm from the
openstack instance. Modifying the resize workflow
to use the above mentioned methods.

Closes-Bug: #1295381

Change-Id: I92acdd5cd00f739d504738413d3b63a2e17f2866
(cherry picked from commit 91ddf85abb8a516cfa2da346b393aa7234660f6c)
Merge "VMware: Fixes the instance resize problem" into milestone-proposed