Merge run-python3-argv-7234: Allow options to run-python3-tests

Author: adiroiban

Reviewer: glyph

Fixes: #7234

Previously run-python3-tests was hard-coded to take only `-v`.  Now it
can take other options (such as `-c` to allow interrupting the tests
with `C-c`).

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@43451 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb