Disable apt-repos 'extras' & 'canonical'. Fix #163

In default ubuntu setup, both apt repositories are commented in
/etc/apt/source.list. In the past, previous ubuntu releases used
in Travis environment did not enable these repositories.
Use hostname specified in attributes.

Change attribute definition to use the hostname from the system.
Use api_token for Librato.
Bump travis_worker version.
Use specific host name for every worker process.
Add more language mappings for the jvm image.
Use worker increment at the end of host name.
Update phpenv with a fix to config-rm.

Fixes travis-ci/travis-ci#999.