repo-review: Extract _process() for error handling

Test: ./repo_review.py -l Verified +1 [query]
Test: ./repo_review.py -m 'Test message' [query]
Test: ./repo_review.py --abandon 'Abandon message' [query]
Change-Id: If986af3a7ace7766e0854d611542deb6a474165b
1 file changed