crowdin: Refactor gerrit.py

* We can separate the code for fetching and submitting
* We can separate parts of the command thats used in more than one
  place
-> That way the code is much cleaner and we can reuse some code later
* Also exit with an error if we can't process a change
* Print errors to stderr

Change-Id: I52527d184ed66554ab4f0dca04919109f9a1bf77
2 files changed