[READY] Fix recursive lookups against IPv6 interface of core master

[kylerisse]

Description of PR

Found issues with DNS lookups over the IPv6 interface only on the core master server.

Previous Behavior

• serverspec tests for recursive DNS didn't exist
• cache network config for core master had the wrong /64 defined

New Behavior

• serverspec tests for recursive DNS now exist
• cache network config for core master has been corrected

Tests

• serverspec locally
• this PR branch being applied to core master after closing keynote is complete.

[sarcasticadmin]

thanks for helping track this down!