Tests now call busy_retry() and sleeping_retry() with SHORT_TIMEOUT
or LONG_TIMEOUT (of test.support), rather than hardcoded constants.
Add also WAIT_ACTIVE_CHILDREN_TIMEOUT constant to
_test_multiprocessing.
* Replace time.sleep(0.010) with sleeping_retry() to
use an exponential sleep.
* support.wait_process(): reuse sleeping_retry().
* _test_eintr: remove unused variables.
* Add run_test_script() function to test.support.script_helper.
* Rename Lib/test/eintrdata/eintr_tester.py to
Lib/test/_test_eintr.py.
* test_eintr.py uses run_test_script().
Victor Stinner