scripts/oe-selftest: return based on the test results

Regardless if the tests passed or not the script returned 0,
which isn't what one would expect.

(From OE-Core rev: c38f943c7fbb1fc077c875099dce8f73f41043b9)

Signed-off-by: Stefan Stanacar <stefanx.stanacar@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/oe-selftest

@@ -144,8 +144,10 @@ def main():
     add_include()
     result = runner.run(suite)
     log.info("Finished")
-
-    return 0
+    if result.wasSuccessful():
+        return 0
+    else:
+        return 1
 
 if __name__ == "__main__":
     try: