mgr/cephadm: be aware of host's shortname and FQDN

mgr/cephadm: be aware of host's shortname and FQDN

The idea is to gether the shortname and FQDN as part
of gather-facts, and then if we ever try to check if a certain
host is in our internal inventory by hostname, we can check
these other known names. This should avoid issues where
we think a hostname specified by FQDN is not in our
inventory because we know the host by the shortname
or vice versa.

Fixes: https://tracker.ceph.com/issues/58738
Signed-off-by: Adam King <adking@redhat.com>