Verify that neither the Swift container or Mistral environment exist
Verify that neither the Swift container or Mistral environment exist

Without this check it is possible for create plan to get into a
partial state. If the Mistral environment exists, but the swift
container doesn't then it will create the container and error
when attempting to create the environment. There is still a
possibility of a race condition, but this verification greatly
reduces that risk.

Change-Id: I18dee67c5935248a32b3b90241e3bbdd02034677
Closes-Bug: 1613196

openstack/tripleo-common,openstack/tripleo-common