Add sign_apex.py that signs a given APEX file.

This CL moves SignApex() from sign_target_files_apks into apex_utils,
and adds sign_apex that allows signing a standalone APEX file directly.

Test: Run the following command and check the output file.
$ build/make/tools/releasetools/sign_apex.py \
     -v \
     --container_key \
         build/make/target/product/security/testkey.x509.pem \
     --payload_key external/avb/test/data/testkey_rsa4096.pem \
     --payload_extra_args \
         "--signing_helper_with_files ./signing-helper.sh" \
     foo.apex \
     signed-foo.apex
Test: Run sign_target_files_apks.py on crosshatch target_files.zip.
Change-Id: I4b2422fd5cb1c60a3aa94511475e2a0e5b1666ca
diff --git a/tools/releasetools/sign_target_files_apks.py b/tools/releasetools/sign_target_files_apks.py
index 24ee91b..7de0978 100755
--- a/tools/releasetools/sign_target_files_apks.py
+++ b/tools/releasetools/sign_target_files_apks.py
@@ -403,77 +403,6 @@
   return data
 
 
-def SignApex(apex_data, payload_key, container_key, container_pw,
-             codename_to_api_level_map, signing_args=None):
-  """Signs the current APEX with the given payload/container keys.
-
-  Args:
-    apex_data: Raw APEX data.
-    payload_key: The path to payload signing key (w/ extension).
-    container_key: The path to container signing key (w/o extension).
-    container_pw: The matching password of the container_key, or None.
-    codename_to_api_level_map: A dict that maps from codename to API level.
-    signing_args: Additional args to be passed to the payload signer.
-
-  Returns:
-    The path to the signed APEX file.
-  """
-  apex_file = common.MakeTempFile(prefix='apex-', suffix='.apex')
-  with open(apex_file, 'wb') as apex_fp:
-    apex_fp.write(apex_data)
-
-  APEX_PAYLOAD_IMAGE = 'apex_payload.img'
-  APEX_PUBKEY = 'apex_pubkey'
-
-  # 1a. Extract and sign the APEX_PAYLOAD_IMAGE entry with the given
-  # payload_key.
-  payload_dir = common.MakeTempDir(prefix='apex-payload-')
-  with zipfile.ZipFile(apex_file) as apex_fd:
-    payload_file = apex_fd.extract(APEX_PAYLOAD_IMAGE, payload_dir)
-
-  payload_info = apex_utils.ParseApexPayloadInfo(payload_file)
-  apex_utils.SignApexPayload(
-      payload_file,
-      payload_key,
-      payload_info['apex.key'],
-      payload_info['Algorithm'],
-      payload_info['Salt'],
-      signing_args)
-
-  # 1b. Update the embedded payload public key.
-  payload_public_key = common.ExtractAvbPublicKey(payload_key)
-
-  common.ZipDelete(apex_file, APEX_PAYLOAD_IMAGE)
-  common.ZipDelete(apex_file, APEX_PUBKEY)
-  apex_zip = zipfile.ZipFile(apex_file, 'a')
-  common.ZipWrite(apex_zip, payload_file, arcname=APEX_PAYLOAD_IMAGE)
-  common.ZipWrite(apex_zip, payload_public_key, arcname=APEX_PUBKEY)
-  common.ZipClose(apex_zip)
-
-  # 2. Align the files at page boundary (same as in apexer).
-  aligned_apex = common.MakeTempFile(
-      prefix='apex-container-', suffix='.apex')
-  common.RunAndCheckOutput(
-      ['zipalign', '-f', '4096', apex_file, aligned_apex])
-
-  # 3. Sign the APEX container with container_key.
-  signed_apex = common.MakeTempFile(prefix='apex-container-', suffix='.apex')
-
-  # Specify the 4K alignment when calling SignApk.
-  extra_signapk_args = OPTIONS.extra_signapk_args[:]
-  extra_signapk_args.extend(['-a', '4096'])
-
-  common.SignFile(
-      aligned_apex,
-      signed_apex,
-      container_key,
-      container_pw,
-      codename_to_api_level_map=codename_to_api_level_map,
-      extra_signapk_args=extra_signapk_args)
-
-  return signed_apex
-
-
 def ProcessTargetFiles(input_tf_zip, output_tf_zip, misc_info,
                        apk_keys, apex_keys, key_passwords,
                        platform_api_level, codename_to_api_level_map,
@@ -538,7 +467,7 @@
         print("           : %-*s payload   (%s)" % (
             maxsize, name, payload_key))
 
-        signed_apex = SignApex(
+        signed_apex = apex_utils.SignApex(
             data,
             payload_key,
             container_key,