tests: pyunit always exiting with 0

As unittest.TextTestRunner().run(suite) doesn't exit the script,
it won't set the exit code, even when some tests are failing.
This means testlib is always interpreting those unittests as passing
even when there are failures.

With this patch we are propagating the error to our CI system (testlib)

Change-Id: I63b7622661a19a9b40243d13b7391e510c2007d4
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/48969
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

tests/run_pyunit.py

@@ -35,8 +35,9 @@
 # (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+import sys
+
 if __name__ == "__main__":
-    import sys
     print("ERROR: This file must be run from gem5.", file=sys.stderr)
     sys.exit(1)
 
@@ -47,5 +48,9 @@ if __name__ == "__m5_main__":
     tests = loader.discover("pyunit", pattern='pyunit*.py')
 
     runner = unittest.runner.TextTestRunner(verbosity=2)
-    runner.run(tests)
+    result = runner.run(tests)
+    if result.wasSuccessful():
+        sys.exit(0)
+    else:
+        sys.exit(1)