Fix VMwareVCDriver to support multi-datastore

This fixes the issue of VCDriver selecting the first datastore of
Cluster while provisioning instances. User can provide a regex to
match with the desired datastores.

Fixes: bug #1104994

(cherry picked from commit 9579ece88962ec86bd54d7930c764105e38f5db6)

Conflicts:

        etc/nova/nova.conf.sample
        nova/tests/test_vmwareapi.py
        nova/tests/test_vmwareapi_vm_util.py
        nova/virt/vmwareapi/driver.py
        nova/virt/vmwareapi/vm_util.py
        nova/virt/vmwareapi/vmops.py

Change-Id: I319b0d8afd03e9fef00ea0c8c799790714685104
Merge "Fix VMwareVCDriver to support multi-datastore" into stable/grizzly
Merge branch 'stable/grizzly' of https://github.com/openstack/nova into kbenton/ivssupport_grizzly