Add an option --first-job-group
Add an option --first-job-group

...to indicate that only the first group of jobs is to be
executed. This is useful for utilization-based balancing,
to allow the situation to be reevaluated after the first
set of non-conflicting moves.

Signed-off-by: Klaus Aehlig <4ce51de36d9068cd7db2eec1151e0f3f95419008@google.com>
Reviewed-by: Hrvoje Ribicic <be5828fca31f89218048bec4189e30a581aa65da@google.com>

dimara/ganeti,leshchevds/ganeti,grnet/snf-ganeti,mbakke/ganeti,ganeti/ganeti,mbakke/ganeti,leshchevds/ganeti,andir/ganeti,yiannist/ganeti,ganeti/ganeti,bitemyapp/ganeti,yiannist/ganeti,andir/ganeti,grnet/snf-ganeti,onponomarev/ganeti,bitemyapp/ganeti,andir/ganeti,dimara/ganeti,leshchevds/ganeti,onponomarev/ganeti,mbakke/ganeti,yiannist/ganeti,ganeti/ganeti