scripts/unit-test.py: Add ability to run `make check` N times

This is useful for catching intermittent failures in test suites when
doing manual (non-CI) runs.

Tested: Reworked run-unit-test-docker.sh, ran and observed multiple runs
of `make check`.

Change-Id: Idf4d81a27b59cc377b2fdc0a672490befbdc4816
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
1 file changed