xfstests: Reintroduce configurable test expunging.

xfstests: Reintroduce configurable test expunging.

It is definitely handy to be able to disabdle certain tests (e.g. tests that are
known to hang or crash the test machine on certain kernels), so re-introducing
the capability of avoiding certain tests just by placing them in a file is
useful.

Introduce a command line option to specify the expunged file name. The file will
exist in each tests/* sub-directory so that only the testname is required, and
can be managed independently. The use of a command line parameter allows
multiple expunge files to exist simultaneously in the one xfstests tree which
simplifies management of a source repository used for multiple versions of a
distro.

Typical usage:

$ cat tests/generic/3.0-stable-avoid
280
$ sudo ./check -X 3.0-stable-avoid generic/280
FSTYP         -- xfs (debug)
PLATFORM      -- Linux/x86_64 test-1 3.0.39-dgc+
MKFS_OPTIONS  -- -f -bsize=4096 /dev/vdb
MOUNT_OPTIONS -- /dev/vdb /mnt/scratch

generic/280     [expunged]
Passed all 0 tests
$

Eventually we should be able to automate setting up expunged files based on
distro release or kernel version through this infrastructure.

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