LU-17251 tests: try to fix test_rr_alloc again

LU-17251 tests: try to fix test_rr_alloc again

Try to fix parallel-scale test_rr_alloc again:
- ensure that the test directory is striped over all MDTs to
  maximize the number of precreated objects available
- ensure the FID SEQ has OIDs to not run out during this test,
  which caused some OSPs to run out of objects during creation

Add debugging to understand issue more if it continues to fail:
- print lfs df, lfs df -i at start and error to show imbalance
- delete files only in cleanup_rr_alloc() so distribution can be shown

Clean up test script to ensue SEQ is large enough to run test.

Test-Parameters: trivial
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testgroup=review-dne-part-9 env=RACER_EXCEPT="1 2"
Test-Parameters: testlist=parallel-scale env=ONLY=rr_alloc,ONLY_REPEAT=50
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I636a488e575d27ac235749911f171d5e1e33e310
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56853
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>