Add performance data to leap_cli checkmk output
right now, the output only tell if the check was successful or not
root@donkey:~# /srv/leap/bin/run_tests --checkmk --test Webapp/Can_sync_Soledad? 0 Webapp/Can_sync_Soledad? - Success
following https://mathias-kettner.de/checkmk_localchecks.html the output should contain performance data that we can graph over time, i.e. to see how much faster the soledad sync gets.
i.e. sth like this:
root@donkey:~# /srv/leap/bin/run_tests --checkmk --test Webapp/Can_sync_Soledad? 0 Webapp/Can_sync_Soledad? overall_time=1.56;3;5|docs_per_sec=3.12;5;6 Success
(from redmine: created on 2016-09-05)