Support use of timeout command in Action:run_cmd

Closes: #205 - Implement support for kill_after which uses
timeout with max_end_time but adds an explicit kill signal
if the process does not end.

Signed-off-by: Neil Williams <neil.williams@linaro.org>
13 jobs from killafter in 9 minutes and 35 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #25468
amd64
dispatcher-debian-10

00:02:41

passed #25466
amd64
dispatcher-debian-9

00:03:07

passed #25469
amd64
server-debian-10

00:02:27

passed #25467
amd64
server-debian-9

00:02:57

 
  Analyze
passed #25470
amd64
black

00:00:24

passed #25472
amd64
code_quality

00:00:18

passed #25471
amd64
codestyle

00:00:31

passed #25473
dind amd64 allowed to fail
sast

00:01:50

 
  Build
passed #25476
amd64
amd64/pkg-debian-10

00:01:32

passed #25475
amd64
amd64/pkg-debian-9

00:01:48

passed #25474
amd64
doc

00:01:14

 
  Docker
passed #25477
dind amd64
amd64/lava-dispatcher

00:01:44

passed #25478
dind amd64
amd64/lava-server

00:02:47