Make it easier to interrupt testrunner.py with Ctrl-C.

Ctrl-C now kills the ongoing tests and cancels the remaining ones.

Test: art/test/testrunner/testrunner.py --target --64 --optimizing -j4
Bug: 186530369
Change-Id: I5dbd6932529a4902f4f03e5a36fe3aa8602ea4a6
1 file changed