LU-7665 test: improve sanity 300p

LU-7665 test: improve sanity 300p

Sanity test 300p set OBD_FAIL_OUT_ENOSPC once, but it may fail llog
operation (not critical), therefore subsequent mkdir succeeds. Change
the fail_loc to always fail so the test can be more robust.

Lustre-change: https://review.whamcloud.com/54625
Lustre-commit: ac04484c1beec9f46d1256e8ea236f24073344af

Test-Parameters: trivial
Test-Parameters: mdscount=2 mdtcount=4 testlist=sanity
Test-Parameters: mdscount=2 mdtcount=4 testlist=sanity
Test-Parameters: mdscount=2 mdtcount=4 testlist=sanity
Test-Parameters: mdscount=2 mdtcount=4 testlist=sanity
Test-Parameters: mdscount=2 mdtcount=4 testlist=sanity
Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I128ce39aaf97e1785a8c135a696d0b404b48a2a8
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56941
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>