Merge branch 'stable-3.0' into stable-3.1

* stable-3.0:
  GerritRestApi: Use UTF_8 from StandardCharsets instead of Guava
  Fix NPE in PushResultProcessing
  Fix start --wait to track in-flight collisions and to not fail
  Improve URLmatching to match real Urls
  Convert PushResultProcessing to an interface

Change-Id: I623b58397d4ae9b9cc6c7038c992225eb33bc3b7