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
diff --git a/tools/releasetools/test_ota_from_target_files.py b/tools/releasetools/test_ota_from_target_files.py
index 466fde1..bb0236b 100644
--- a/tools/releasetools/test_ota_from_target_files.py
+++ b/tools/releasetools/test_ota_from_target_files.py
@@ -1233,6 +1233,7 @@
     """Uses testdata/payload_signer.sh as the external payload signer."""
     common.OPTIONS.payload_signer = os.path.join(
         self.testdata_dir, 'payload_signer.sh')
+    os.chmod(common.OPTIONS.payload_signer, 0o700)
     common.OPTIONS.payload_signer_args = [
         os.path.join(self.testdata_dir, 'testkey.pk8')]
     payload_signer = PayloadSigner()