tests: allow unstable tests to be marked with CONFIG+=insignificant_test

Marking a test with CONFIG+=insignificant_test will cause the exit code
of the test to be discarded during `make check'.  This is intended to be
used for tests which are valuable to run, but are known to be unstable
and are not feasible to immediately fix.

Reviewed-by: Jason McDonald
Change-Id: I50a712c33c2ebb0af39f1ea0bf2adef7f0936425
(cherry picked from commit b0a5a988900b777cb08012408eb108512a3e873b)

Author: Rohan McGovern

mkspecs/features/testcase.prf

@@ -38,6 +38,10 @@ embedded:       check.commands += -qws
 
 # Allow for custom arguments to tests
 check.commands += $(TESTARGS)
+
+# If the test is marked as insignificant, discard the exit code
+insignificant_test:check.commands = -$${check.commands}
+
 QMAKE_EXTRA_TARGETS *= check
 
 !debug_and_release|build_pass {