LU-11912 tests: consume precreated objects in parallel

LU-11912 tests: consume precreated objects in parallel

Run the force_new_seq_all() file creations to run in parallel, since
this can take a significant amount of time when there are multiple
MDTs and OSTs (up to 1000s for 4x MDTs and 8x OSTs).

Lustre-change: https://review.whamcloud.com/51292
Lustre-commit: 656fc937cfd3fc3b65cb21a7f93a6bd4cc07fc0e

Test-Parameters: trivial testlist=replay-dual mdscount=2 mdtcount=4
Test-Parameters: testlist=replay-ost-single mdscount=2 mdtcount=4
Test-Parameters: testlist=replay-single mdscount=2 mdtcount=4
Test-Parameters: testlist=sanity-pfl env=ONLY="0 1 16 27" mdscount=2 mdtcount=4
Fixes: 2fdb1f8d01b9f ("LU-11912 tests: SEQ rollover fixes")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I849370586fe320d1f7df069f0b83980449658d97
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Alex Deiter <alex.deiter@gmail.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/51496
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>