Get the vCenter password from databag for glance


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: I72f538a16d77cba9c1be9f32e0b37d1ee68e3bbc
Merge "Get the vCenter password from databag for glance"