LU-12100 tests: Use minimum soft qunit limits

LU-12100 tests: Use minimum soft qunit limits

Ensure that we don't create limits that are too small, which would
cause all writes to fail.
Wait for grace period to timeout.

Lustre-change: https://review.whamcloud.com/35667
Lustre-commit: 37e28b7e05a5b1f77fe663f9407436aea312b3b2

Test-Parameters: trivial
Test-Parameters: testlist=sanity-quota
Test-Parameters: testlist=sanity-quota fstype=zfs
Signed-off-by: Nathaniel Clark <nclark@whamcloud.com>
Change-Id: I9342272615ca9c252fcc7f77ed8a61030fc9672a
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/36346
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>