Set default branch for git review/gerrit. Switch amulet tests to stable. Switch to using stable charm-helpers branch. Change-Id: Ib4096a4652c78d1378bafd2505d7fc2df360fc96
Set default branch for git review/gerrit. Switch amulet tests to stable. Switch to using stable charm-helpers branch. Change-Id: Ib4096a4652c78d1378bafd2505d7fc2df360fc96