check: add CLI option to repeat tests

check: add CLI option to repeat tests

Frequently when trying to reproduce a problem I want to run a set of
specific tests in a loop, over and over again. I run fstests from a
set of run scripts that have non-trivial overhead (e.g. patterning
block devices before the runs start), so if all I want to do is run
the same test 100x, using a shell loop over the entire run
scripts reduces the iteration rate substantially.

Hence add an option to check to allow fstests to loop a number of
times over the configured test set without stopping.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>