xfstests: update method to set TESTS_SUBDIRS in tests/Makefile.
make install support common/ and tests/ dirs (V4)
* reposted for current top of tree changes. [rjohnston@sgi.com]
* use the neater way by Dave to get the TESTS_SUBDIRS in tests/Makefile.
Signed-off-by: Wang Sheng-Hui <shhuiw@gmail.com>
[rjohnston@sgi.com Reposted for current top of tree changes] Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Rich Johnston <rjohnston@sgi.com>