relesetools: Support running all the unittests with atest.

All the unittests will be built into releasetools_test. One can run the
tests with `atest releasetools_test` or the traditional way
`test_utils.py`. The atest way is recommended, which additionally builds
the required tools.

With the current support in Soong, we can't pack the built tools into
releasetools_test yet. So running `releasetools_test` alone in clound
would fail. Follow-up CLs will address the issue in order to deploy the
tests with TEST_MAPPING.

Bug: 112080715
Test: `atest releasetools_test`
Change-Id: Ica95517a5ab326f4e58fc57c6c2c276cfe882f3c

tools/releasetools/test_apex_utils.py

@@ -56,8 +56,10 @@ class ApexUtilsTest(test_utils.ReleaseToolsTestCase):
 
   def test_SignApexPayload_withSignerHelper(self):
     payload_file = self._GetTestPayload()
+    signing_helper = os.path.join(self.testdata_dir, 'signing_helper.sh')
+    os.chmod(signing_helper, 0o700)
     payload_signer_args = '--signing_helper_with_files {}'.format(
-        os.path.join(self.testdata_dir, 'signing_helper.sh'))
+        signing_helper)
     apex_utils.SignApexPayload(
         payload_file,
         self.payload_key,