fstests: groupfile generation needs force overwrite

fstests: groupfile generation needs force overwrite

Having built fstests as root as part of a run script, I get failures
then trying to run it as a user because of the group list
generation. The issue occurs because the group list files are owned
by root, and so I get an interactive prompt to overwrite them such
as:

Building btrfs
 [GROUP] /home/dave/src/xfstests-dev/tests/btrfs/group.list
mv: replace 'group.list', overriding mode 0644 (rw-r--r--)? y
Building ceph
 [GROUP] /home/dave/src/xfstests-dev/tests/ceph/group.list
mv: replace 'group.list', overriding mode 0644 (rw-r--r--)? y
Building cifs
 [GROUP] /home/dave/src/xfstests-dev/tests/cifs/group.list
mv: replace 'group.list', overriding mode 0644 (rw-r--r--)? y
Building ext4
 [GROUP] /home/dave/src/xfstests-dev/tests/ext4/group.list
...

Use 'mv -f' to ignore such trivial issues so that the new group
lists are written correctly.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>