LP#1711194 osrf_config --diagnostic reports max-children

LP#1711194 osrf_config --diagnostic reports max-children

--diagnostic output shows the maximum number of allowed drones per
service along with the active drone count.  Additionally, a usage
percentage value is displayed.

E.g.

$ /openils/bin/osrf_control -l --diagnostic

* open-ils.acq   [1581] uptime=00:35 cputime=00:00:00 #drones=1/15 6%
* open-ils.actor [1629] uptime=00:35 cputime=00:00:00 #drones=2/15 13%

Signed-off-by: Bill Erickson <berickxx@gmail.com>
Signed-off-by: Chris Sharp <csharp@georgialibraries.org>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>