Make ipaclient.discovery usable from command line
For debugging and testing make it possible to run a simple domain
discovery from the command line
```
$ python3 -m ipaclient.discovery demo1.freeipa.org
realm DEMO1.FREEIPA.ORG (Discovered from LDAP DNS records in ipa.demo1.freeipa.org)
domain demo1.freeipa.org (Discovered LDAP SRV records from demo1.freeipa.org)
basedn dc=demo1,dc=freeipa,dc=org (From IPA server ldap://ipa.demo1.freeipa.org:389)
server ipa.demo1.freeipa.org (Discovered from LDAP DNS records in ipa.demo1.freeipa.org)
servers ['ipa.demo1.freeipa.org']
Success
$ python3 -m ipaclient.discovery freeipa.org
realm None
domain None
basedn None
server None
servers []
NO_LDAP_SERVER
```
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>