LU-11572 tests: make sanity-hsm test_260c reliable

LU-11572 tests: make sanity-hsm test_260c reliable

When the coordinator restarts, its first run does housekeeping.
For the following `loop_period' seconds, it will not run in
housekeeping mode.

This patch uses this to improve the reliability of sanity-hsm
test_260c.

Test-Parameters: trivial testlist=sanity-hsm,sanity-hsm,sanity-hsm
Signed-off-by: Quentin Bouget <quentin.bouget@cea.fr>
Change-Id: I8eeb8b6856d91b69495d592cdd1cb5f091b1cc2b
Reviewed-on: https://review.whamcloud.com/33478
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>