Configurable log levels

Allow ssh log_level to be set - this will help to debug connection
issues.

lib/mrsk/configuration.rb

@@ -172,7 +172,7 @@ class Mrsk::Configuration
       service_with_version: service_with_version,
       env_args: env_args,
       volume_args: volume_args,
-      ssh_options: ssh.options,
+      ssh_options: ssh.to_h,
       sshkit: sshkit.to_h,
       builder: builder.to_h,
       accessories: raw_config.accessories,

lib/mrsk/configuration/ssh.rb

@@ -1,4 +1,6 @@
 class Mrsk::Configuration::Ssh
+  LOGGER = ::Logger.new(STDERR)
+
   def initialize(config:)
     @config = config.raw_config.ssh || {}
   end
@@ -16,9 +18,21 @@ class Mrsk::Configuration::Ssh
   end
 
   def options
-    { user: user, proxy: proxy, auth_methods: [ "publickey" ], keepalive: true, keepalive_interval: 30 }.compact
+    { user: user, proxy: proxy, auth_methods: [ "publickey" ], logger: logger, keepalive: true, keepalive_interval: 30 }.compact
+  end
+
+  def to_h
+    options.except(:logger).merge(log_level: log_level)
   end
 
   private
     attr_accessor :config
+
+    def logger
+      LOGGER.tap { |logger| logger.level = log_level }
+    end
+
+    def log_level
+      config.fetch("log_level", :fatal)
+    end
 end