Get the vCenter password from databag for cinder

1. Add new attribute openstack_vmware_secret_name to indicate the
databag secret key
2. Get the password from databag if dev mode is false
3. Update the test cases

Implements: blueprint vmware-password-databag

Change-Id: Id6872d38c255067a4991aceaa0bf6fb400cce1c8
Merge "Get the vCenter password from databag for cinder"