Add a command to trigger entrypoint cache creation
Add a command to trigger entrypoint cache creation

stevedore will cache the entrypoint scan when needed. Since we
just installed the things here, do an openstack --help to cause
the entrypoints to get scanned at build time and for the cache
file to be written into the container image.

Change-Id: I73502be6d68c4a38561c9524b4def3c6a6f61ac6

openstack/python-openstackclient,openstack/python-openstackclient