Support for VMware store to use multiple datastore backends.
Spec (approved):
https://review.openstack.org/#/c/146723/
tl;dr:
1. Adds a new config option vmware_datastores to configure
multiple datastores.
2. Implements a selection logic based on priority to choose
from the list of datastores.
3. Modifies StoreLocation parsing logic to identify datastore
related info from location URI.
DocImpact
Implements-Blueprint: vmware-store-multiple-datastores
Change-Id: I176f1143cd2d9b0a01a0f4f4256e7ac7d9b09afd
aa10f66ee0