LU-8526 tests: ensure all OSTs active for allocations

LU-8526 tests: ensure all OSTs active for allocations

This patch ensures that all OSTs are active to be selected
for objids allocations. This will allow for random selection
of OSTs during setstripe to be effective.
To do so, wait_osts_up() has been exported from conf-sanity
to test-framework to become part of the generic functions
set and be used from any tests suites, and particularly in
replay-single/test_90 sub-test.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Id5db31948ab86c1b3c2bc289191917ed3e8aadf8
Reviewed-on: https://review.whamcloud.com/23148
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>