Add quote to the signing arguments when passing to apexer

We should add quote when passing the signing arguments to apexer. So
the final argument whould look like
apexer ... --signing_args "--signing_helper_with_files=%path"

And the argument parser in avbtool will eventually parse the
"--signing_helper_with_files" correctly.

Bug: 148627666
Test: unittest pass, run a smoke sign_target_files_apk with signing arguments
Change-Id: Ie203d26a508cb98ca94e6c364a2640b681ad79f2
diff --git a/tools/releasetools/apex_utils.py b/tools/releasetools/apex_utils.py
index 4ca0917..4fac6f3 100644
--- a/tools/releasetools/apex_utils.py
+++ b/tools/releasetools/apex_utils.py
@@ -157,8 +157,10 @@
                   os.getenv('PATH')]
     for key, val in arguments_dict.items():
       repack_cmd.extend(['--' + key, val])
+    # Add quote to the signing_args as we will pass
+    # --signing_args "--signing_helper_with_files=%path" to apexer
     if signing_args:
-      repack_cmd.extend(['--signing_args', signing_args])
+      repack_cmd.extend(['--signing_args', '"{}"'.format(signing_args)])
     # optional arguments for apex repacking
     manifest_json = os.path.join(apex_dir, 'apex_manifest.json')
     if os.path.exists(manifest_json):