Subprocess32 provides a backport of python 3.2's subprocess module,
which has a timeout parameter for Popen.communicate. When the timeout
runs out then an exception is raised, and when that exception is caught
we can kill the process.

This is fairly similar to the way the current timeout mechanism works,
except that the current mechanism is not thread safe. Since one of the
major features of piglit is that it offer's processes isolated
concurrency of tests, it makes sense to make the effort to provide a
timeout mechanism that supports concurrency. Unfortunately there isn't a
good cross platform mechanism for this in python 2.x, even with
subprocess 32 only *nix systems are supported, not windows.

The big advantage of this is it allows consistent behavior between
python 2.x and 3.x as we look toward the future and the possibility of
using a hybrid approach to transition to python 3.x while maintaining
2.x support until it's not needed.

This patch look pretty substantial. It's not as big as it looks, since
it adds some fairly big tests.

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>