xfs_quota: allow individual timer extension

xfs_quota: allow individual timer extension

The only grace period which can be set via xfs_quota today is for id 0,
i.e. the default grace period for all users.  However, setting an
individual grace period is useful; for example:

 Alice has a soft quota of 100 inodes, and a hard quota of 200 inodes
 Alice uses 150 inodes, and enters a short grace period
 Alice really needs to use those 150 inodes past the grace period
 The administrator extends Alice's grace period until next Monday

vfs quota users such as ext4 can do this today, with setquota -T

xfs_quota can now accept an optional user id or name (symmetric with
how warn limits are specified), in which case that user's grace period
is extended to expire the given amount of time from now().

To maintain compatibility with old command lines, if none of
[-d|id|name] are specified, default limits are set as before.

(kernelspace requires updates to enable all this as well.)

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>