Add container name env var for containers

Because the container name is generated it isn't possible to
determine this inside the container.

This adds the MRSK_CONTAINER_NAME env var when running the
container so it can be read by the service running inside the
container.

lib/mrsk/commands/app.rb

@@ -7,6 +7,7 @@ class Mrsk::Commands::App < Mrsk::Commands::Base
       "--restart unless-stopped",
       "--log-opt", "max-size=#{MAX_LOG_SIZE}",
       "--name", service_with_version_and_destination,
+      "-e", "MRSK_CONTAINER_NAME=\"#{service_with_version_and_destination}\"",
       *role.env_args,
       *config.volume_args,
       *role.label_args,