zuul: client to easily query Gearman server

Zuul spawn a Gearman server which can be queried over TCP with a
oneliner such as:

  echo status|nc -q 3 localhost 4730

Documented at:
https://www.mediawiki.org/wiki/Continuous_integration/Zuul#Debugging

I find it cumbersome to remember the possible commands 'status' and
'workers', make it a python script so ones can easily query the server.

It defaults to querying the server on 127.0.0.1, so only install the
utility on host having zuul::server (gallium.wikimedia.org).

Script tested there and working fine, simply:

 zuul-gearman.py status
 zuul-gearman.py workers

Change-Id: I9be8e020aed3ee1b110adc09fe7d5ba9d6162387