fstests: adapt the new test script to our new group tagging scheme

fstests: adapt the new test script to our new group tagging scheme

Now that we autogenerate group files, adapt the new test creation script
to use autogenerated group files and to set the group data in the new
test.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>