test/system/systest_runnable.cc: debugging on start and end

Signed-off-by: Samuel Just <sam.just@inktank.com>
Merge pull request #2252 from ceph/wip-9087

test/system/systest_runnable.cc: debugging on start and end

Reviewed-by: Sage Weil <sage@redhat.com>
Merge remote-tracking branch 'upstream/next'