In some situations it may be helpful to populate the fact cache on
demand. The 'kolla-ansible gather-facts' command may be used to do this.

One specific case where this may be helpful is when running kolla-ansible
with a --limit argument, since in that case hosts that match the limit
will gather facts for hosts that fall outside the limit. In the extreme
case of a limit that matches only one host, it will serially gather
facts for all other hosts. To avoid this issue, run 'kolla-ansible
gather-facts' without a limit to populate the fact cache in parallel
before running the required command with a limit.

Change-Id: I79db9bca23aa1bd45bafa7e7500a90de5a684593