Add RecommendationPlugin for Cloud Print

Reuses already existing infrastructure. The mMDNSFilteredDiscovery lambda
is called for every network service that supports #PRIVET_SERVICE. Then
the plugin checks the txt fields to make sure the printer is valid. The
check is not complete but good enough to make sure this is either a
cloud print capable printer or something that tries really hard.

Test: Connected to network with three printers, 2 GCP capable. Found the
      two printers
Fixes: 35766193
Change-Id: I7c9180c8c154fa092fec5b943a94bad77da74c86