Set default branch for git review/gerrit. Switch amulet tests to stable. Switch to using stable charm-helpers branch. Change-Id: I185ae8272386755de2a26467ab4f8f41fda732ec
Set default branch for git review/gerrit. Switch amulet tests to stable. Switch to using stable charm-helpers branch. Change-Id: I185ae8272386755de2a26467ab4f8f41fda732ec