Update get_quota to handle grace values

Update get_quota to support output from the `quota` command that
includes values in the grace columns. These columns have been empty for
ext4 volumes, but with xfs volumes, they can have a value, and that was
causing get_quota to return incorrect values for certain fields. Add the
-p flag to the quota call so the grace columns always have a value.

Fix bug 1129394.
Merge pull request #5706 from ncdc/xfs-quota

Merged by openshift-bot