CI: travis: workaround 127.0.1.1 not assigned with loopback

This is so as to counterweight unfortunate change
https://github.com/travis-ci/travis-cookbooks/commit/6c575d5d55c08e3a0c046dc7de2aa5d5b38e0b63
that made proper hostnames be mapped from 127.0.1.1 address rather than
127.0.0.1 (properly assigned to loopback interface), hence (likely)
caused "hostname -i" return that other address that is normally not
assigned to loopback (and hence booth cannot identify "itself" within
configured sites, leading to spurious test suite failure).