fsstress: add the -c option

fsstress: add the -c option

This option causes fsstress to delete the test directory between each
run.  This is the opposite from the ltp version of fsstress, which
deletes the test directory by default, and the -c option caused ltp's
fsstress _not_ to delete the test directory.

It can be useful to be able to have the same test behavior as ltp
version, and although reversing the sense of the option is
unfortunate, it also reserves the -c option, which makes it a bit
easier if we want to eventually have one version which is a superset
of the xfstest and ltp version of fsstress.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>