Checks to make sure that a docker container is running before determining whether or not the port is in use. This prevents the a port on an inactive container from being treated as if it is use. Fixes https://github.com/hashicorp/vagrant/issues/13110
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.
Generate proto
grpc_tools_ruby_protoc -I . --ruby_out=gen/plugin --grpc_out=gen/plugin ./plugin_server.proto