Some edits for help strings

Some edits for neutron help strings as noticed by Lana during review of
this patch:
https://review.openstack.org/#/c/102900/

Change-Id: I4f6cbb3ced85e15c5f4f716aad630090955de31b
Co-Authored-By: Lana Brindley <openstack@lanabrindley.com>
Merge "Some edits for help strings"