xfstests: 310 fails with existing directory error

xfstests: 310 fails with existing directory error

Test 310 fails with:

mkdir: cannot create directory `/mnt/test/tmp': File exists

$TEST_DIR is persistent, so test directories need to be created with
"mkdir -p" so they don't fail if the directory already exists.

Many other things need fixing, too.
	- Tests should define directories they use on $TEST_DIR by
	  their sequence number, not generic names.

	- Use a variable for the directory the test runs in
	  ($SEQ_DIR, in this case) to avoid having to manually code
	  it everywhere.

	- New binaries need to be added to .gitignore.

	- Return status for shell functions is 0 for success,
	  non-zero for failure.

	- Setting status=0 if there is no failure in the first test
	  means that even if the second test fails, the test will
	  still pass. Change the test to use "_fatal" when a kernel
	  bug is detected, and only set status=0 when the entire
	  test has finished.

	- reduce the default runtime by to roughly a minute and
	  scale it with the stress load factor variables. In most
	  cases, this test is never going to hit problems (as
	  they've already been fixed) so running it for ~4 minutes
	  is mostly a waste of time...

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