LU-8879 tests: speed up copytool_cleanup() in sanity-hsm

LU-8879 tests: speed up copytool_cleanup() in sanity-hsm

This patch implements the following improvements:

 - The coordinator now wakes up when hsm_control is set to 'shutdown'

 - The wait_copytools() function in sanity-hsm uses a polling
   mechanism to detect when all running copytools are killed.
   It used to sleep before the first check, even though that check
   would pass most of the time. This has been fixed.

 - wait_copytools() used to sleep for 2s between its checks. It now
   sleeps for 0.1s, 0.2s, 0.4s, 0.8s, 1.6s, 3.2s, 3.2s, 3.2s, ...
   until it times out.

Considering how often the wait_copytools() function is called in
sanity-hsm, this patch should represent a noticeable speed-up.

Test-Parameters: trivial testlist=sanity-hsm
Signed-off-by: Quentin Bouget <quentin.bouget@cea.fr>
Change-Id: Ia460df59a724caaa194565dd7af402c8c617f40e
Reviewed-on: https://review.whamcloud.com/24025
Reviewed-by: Henri Doreau <henri.doreau@cea.fr>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jean-Baptiste Riaux <riaux.jb@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>