Bug 1549380 - Increase gtest process timeout from 20 minutes to 40 minutes; r=jmaher

Increasing the timeout avoids a perma-fail on linux64/ccov and leaves room for the
test suite to grow on all platforms.

Differential Revision: https://phabricator.services.mozilla.com/D30083

--HG--
extra : moz-landing-system : lando

testing/gtest/rungtests.py

@@ -21,7 +21,7 @@ log = mozlog.unstructured.getLogger('gtest')
 
 class GTests(object):
     # Time (seconds) to wait for test process to complete
-    TEST_PROC_TIMEOUT = 1200
+    TEST_PROC_TIMEOUT = 2400
     # Time (seconds) in which process will be killed if it produces no output.
     TEST_PROC_NO_OUTPUT_TIMEOUT = 300