Move ValidateHost to opts
Squashed implementation of groups
Reorder methods in group.go
Move sorting tests to ./api
Start on integration tests for groups
Fix bug in group deletion: graph wasn't being purged correctly
Integration test for creating a container in a group and starting it
Rename 'groups list' to 'groups ls'
Integration test for `docker groups create -`

Fix panic when there's no HostConfig in group container JSON
Implement -t flag for 'docker groups stop'
Clean up group tests
Implement --recreate flag and add test for volumes
Extract build() method from cli.CmdBuild()
Implement composition