LU-11489 tests: retry power off/on several times

Sometimes we have a BMC hangup for ~1 minute.
Patch improves ha.sh to try power off/on several
times with delay $ha_power_delay default 60 sec.

Test-Parameters:trivial
Signed-off-by: Elena Gryaznova <c17455@cray.com>
Cray-bug-id: LU-6486
Reviewed-by: Andrew Perepechko <c17827@cray.com>
Reviewed-by: Alexander Boyko <c17825@cray.com>
Change-Id: Id192e2a39a229979484b0d209fa8fdc5fafbbfc6
Reviewed-on: https://review.whamcloud.com/33332
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>