[deployer] Fix service name for PowerDNS when updating service ip address
[deployer] Fix service name for PowerDNS when updating service ip address

Deployer updates addresses found at the microBosh spec with the assigned
microBosh address. For PowerDNS it should look for dns["address"] instead
of powerdns["address"].

barthy1/bosh,barthy1/bosh,barthy1/bosh,barthy1/bosh