On Linux, skip tests using multiprocessing if the current user cannot
create a file in /dev/shm/ directory. Add the
skip_if_broken_multiprocessing_synchronize() function to the
test.support module.
bpo-30339, bpo-33913:
* Increase timeout from 10 seconds to 1 minute in
test_source_main_skipped_in_children source of
test_multiprocessing_main_handling.
* Replace time.time() with time.monotonic().
* On timeout, include the duration in the error message.
This should appease the OpenIndiana buildbot.
Also lengthened the worst case timeout to try to eliminate
the inconsistent failure on one of the Windows 7 buildbots.
Thanks to Christian Heimes for noting the buildbot failures and
to Zachary Ware for providing the patch to make the new tests
play nice with both other platforms and unittest test discovery