Allow asynchronous fetch calls

To improve user experience add functionality to decide for which refs
git fetch operation will be called asynchronously.

Also only git fetch operation should be executed asynchronously, sending
ref content as a payload should be synchronous.

Bug: Issue 13340
Change-Id: Iba08f1cc140f4d88016e6850abc51cd658c432e5
12 files changed
tree: e08397fde7653e38b7917b92d586e52d78b4044c
  1. src/
  2. BUILD
  3. Jenkinsfile
  4. LICENSE