LU-18035 tests: enhance root_prj_enable tests

LU-18035 tests: enhance root_prj_enable tests

Add more tests cases at sanity-quota_1i
"Enable project quota enforcement for root":
1. root can't write after enabling root_prj_enable
   if this project has hit its limit
2. root is still able to write at a different
   project ID directory with larger limit

Test-Parameters: testlist=sanity-quota env=ONLY=1i trivial
Fixes: b53438df70e ("LU-15109 tests: different quota and usage relations")
Signed-off-by: Sergey Cheremencev <scherementsev@ddn.com>
Change-Id: I58ce986221b2c970957a05408b20a70301e4f51e
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55757
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>