Move all config validation to main object

lib/mrsk/commands/registry.rb

@@ -1,13 +1,5 @@
 class Mrsk::Commands::Registry < Mrsk::Commands::Base
   def login
-    ensure_credentials_present
     "docker login #{config.registry["server"]} -u #{config.registry["username"]} -p #{config.registry["password"]}"
   end
-
-  private
-    def ensure_credentials_present
-      unless config.registry && config.registry["username"].present? && config.registry["password"].present?
-        raise ArgumentError, "You must configure registry/username and registry/password"
-      end
-    end
 end

lib/mrsk/configuration.rb

@@ -62,6 +62,10 @@ class Mrsk::Configuration
       %i[ service image registry ].each do |key|
         raise ArgumentError, "Missing required configuration for #{key}" unless config[key].present?
       end
+
+      %w[ username password ].each do |key|
+        raise ArgumentError, "Missing required configuration for registry/#{key}" unless config.registry[key].present?
+      end      
     end
 
     def parameterize(param, hash)