xfstests: rework CLI individual test specification

xfstests: rework CLI individual test specification

Now that tests are in separate subdirectories, they cannot be selected purely by
test number on the command line. We need to specify the test by subdir and test
name, so effectively we move to specifying them by regexes on the command line
rather than by expanding a range internally. This is needed to support
non-numeric test names as well, so the change may as well be made here.

This means the command line parsing needs to change from trying to detect tests
by a regex match to a processing loop that simply parses the tests and checks
for there existence. Hence the moment we find an argument that is not a switch
(i.e no preceeding "-"), we move from the arg processing loop to the test name
processing loop. IOWs, tests must be specified last on the command line.

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