provisioners/docker: Ensure checks for whether the container exists / is running works accross multiple Docker versions [GH-2579]
provisioners/docker: Extract container lookup method
Merge pull request #2579 from mitchellh/2579-fix-docker-container-running-check

provisioners/docker: Check for whether the container is running is not working properly
Add missing argument to ProviderVirtualBox::SyncedFolder#driver call

GH-2577 missed passing the `machine` to the `driver` method.
Merge pull request #2586 from tmatilai/2577-synced-folder

provider/virtualbox: add missing argument to ProviderVirtualBox::SyncedFolder#driver call