LU-17251 test: improve parallel-scale rr_alloc test

LU-17251 test: improve parallel-scale rr_alloc test

Added checking for pre-created OST objects and waiting
(maximum 60 seconds) before executing the rr_alloc test.

Test-Parameters: trivial
Test-Parameters: mdtcount=4 mdscount=2 testlist=parallel-scale env=ONLY=rr_alloc,ONLY_REPEAT=8
Test-Parameters: mdtcount=4 mdscount=2 testlist=parallel-scale env=ONLY=rr_alloc,ONLY_REPEAT=8
Test-Parameters: mdtcount=4 mdscount=2 testlist=parallel-scale env=ONLY=rr_alloc,ONLY_REPEAT=8
Test-Parameters: testlist=parallel-scale env=ONLY=rr_alloc,ONLY_REPEAT=8
Test-Parameters: testlist=parallel-scale env=ONLY=rr_alloc,ONLY_REPEAT=8
Test-Parameters: testlist=parallel-scale env=ONLY=rr_alloc,ONLY_REPEAT=8

Signed-off-by: Alex Deiter <adeiter@tintri.com>
Change-Id: Ib604b99138ceccf384476ad2876d9df7cd7d524b
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/52940
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>