LU-17361 tests: reduce lustre-rsync-test/2a+b workload

LU-17361 tests: reduce lustre-rsync-test/2a+b workload

The lustre-rsync-test test_2a and test_2b are copying the dbench
output to the local $TMP filesystem twice and can run into memory
allocation issues on VMs where /tmp is a RAM-based filesystem.
The tests are sufficiently verifying lrsync correctness making
a single copy of the dbench output to the local $TMP filesystem.
Other subtests are verifying that multiple '-t DIR' targets work.

Test-Parameters: trivial
Test-Parameters: testlist=lustre-rsync-test env=ONLY=2a,ONLY_MINUTES=60
Test-Parameters: testlist=lustre-rsync-test env=ONLY=2b,ONLY_MINUTES=60
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ibbc720f30c1146c04760f24bc09e1fe76c762edc
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58930
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Rajeev Mishra <rajeevm@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>