This commit changes the way ports are aggregated in the Docker provider.
Previously ports were aggregated by their "number", but that is not a
truly unique representation. Instead, the protocol is now taken into
account when generating the port map.
Fixes GH-5527
Initial work
commands/up: make sure all names to with_target_vms are strings
providers/docker: create a docker host VM if needed
providers/docker: executor abstraction for driver to eventually support remote
providers/docker: vagrant executor
providers/docker: support creating the machine
providers/docker: status works if host VM is gone
providers/docker: use start fence to get real docker output
core: Call preserves stack ordering
core: support Message post option
providers/docker: Guard some features with HasSSH checks
providers/docker: much better messaging around create/destroy
providers/docker: output the container ID on create
providers/docker: copy the hostmachine Vagrantfile to the data dir
providers/docker: should make host machine before any up action
providers/docker: HandleBox before the host machine
providers/virtualbox: functional_vboxsf to disable vboxsf
providers/virtualbox: synced folder usable method should take 2 args
providers/docker: default machine name to :default
