xfstests: make exclude groups aware of multiple subdirectories

xfstests: make exclude groups aware of multiple subdirectories

Now that there are no tests in the top level directory, the exlude
group functionality no longer works (-x group) as it cannot find
tests to build an initial list of tests. Rework the the exclude
group implementation to operate correctly on the new test locations.

Also, switch from sed to grep for exclusion because sed has problems
distnguishing the '/' in path names from regex control...

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Phil White <pwhite@sgi.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>