kill: find targets for killing a job

kill: find targets for killing a job

In some circumstances teuthology-kill does not unlock the nodes
if it is used to kill just a single job from a run, for example,
while a job in the middle of locking many targets the job_info
does not include targets yet, correspondingly if someone kills
the job at that point, the targets remain in locked state.
This commit address the issue.

Signed-off-by: Kyr Shatskyy <kyrylo.shatskyy@suse.com>