Fix #584: Deal with Arrays for the net list

Author: MG2R

lib/puppet/parser/functions/docker_run_flags.rb

@@ -24,6 +24,8 @@ module Puppet::Parser::Functions
 
     if opts['net'].is_a? String
       flags << "--net #{opts['net']}"
+    elsif opts['net'].is_a? Array
+      flags << "--net #{opts['net'].join(' --net ')}"
     end
 
     if opts['memory_limit']