Add Google and OpenDNS nameservers

There are reports of DNS lookups failing with some frequency,
and they cause build to fail.
(https://github.com/travis-ci/travis-ci/issues/2965)

This commit aims to address it by adding publicly available and
robust name servers from Google and OpenDNS.
Spell check variable name
Auto-merged master into ha-feature-dns-fix on deployment.
Merge pull request #344 from travis-ci/ha-feature-dns-fix

Add Google and OpenDNS nameservers