recursor support

Hi,
This gives support to recursor by changing the settings.yml, I do not know if this feature should be expose and asked on the prompt of the cli.
I would really appreciate if this could be merge! would help us a lot in our project ci_infrastructure_cf.
I tested deploying a microbosh setting the recursor and it worked, I did not tried the recursor feature itself yet. This pull request should not affect previous functionality.

Output: http://pastebin.com/7cxvEmfB#

thanks!
@bonzofenix.