This commit updates all tests to enforce the Python3 executable. This is
necessary because the `assertRegex` function we use was renamed to this
name only in Python 3.2 [1]
For reference:
s;/usr/bin/env python;/usr/bin/env python3;g
[1]: https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertRegex
Running stress_test without arguments runs all of the test-suite 100
times (serially) and stops on first failure.
Passing test names as arguments (stress_test bug.123.t ...) will run
only these.
If 100 is found to be too small or too large pass --repeat <integer>.
Run stress_test -h for more information