Add json key file support for acloud.

Also add an option to let acloud accept json key file path option.

Bug: 111601636
Test: unit test and manually
Change-Id: Idcdcd533018462d648229ae2c6e9d5b9626821b9
Merged-In: Ie5834e683634f82d6e84a76e027adfa91913c59a
diff --git a/public/acloud_main.py b/public/acloud_main.py
index a0e7fc6..feeaa3a 100644
--- a/public/acloud_main.py
+++ b/public/acloud_main.py
@@ -26,6 +26,8 @@
      # If using service account
      service_account_name: "your_account@developer.gserviceaccount.com"
      service_account_private_key_path: "/path/to/your-project.p12"
+     # Or
+     service_account_json_private_key_path: "/path/to/your-project.json"
 
      # If using OAuth2 authentication flow
      client_id: <client id created in the project>