vm docker create: add community option

I based this PR on the changes from https://github.com/MSOpenTech/azure-sdk-tools-xplat/pull/81 because those changes unify the docker and non-docker code paths, making this fix trivial. Please accept https://github.com/MSOpenTech/azure-sdk-tools-xplat/pull/81 first. Not sure if this one will need rebasing then, but I will follow up.