[x509 user] Use $external db for this type of users

Author: Johan De Wit

lib/puppet/provider/mongodb_user/mongodb.rb

@@ -79,7 +79,11 @@ def create
       end
 
       Puppet.debug("XXXXXXXXXX about to create user with command: #{command}")
-      mongo_eval("db.runCommand(#{command.to_json})", @resource[:database])
+      if @resource[:auth_mechanism] == :x509
+        mongo_eval("db.getSiblingDB(\"$external\").runCommand(#{command.to_json}}", @resource[:database])
+      else
+        mongo_eval("db.runCommand(#{command.to_json})", @resource[:database])
+      end
     else
       Puppet.warning 'User creation is available only from master host'