Initial commit for setting up Docker host for Travis CI

Adding 'travis_docker' to run_list should do the job.

WARNING: This is completely untested
Make travis_docker cookbook self-contained
Move travis_docker cookbook to worker_host
Add travis_docker metadata
Prefer remote_file Chef resource to 'wget'
Prefer apt package to another cookbook
Fix package name
Updates to get the Docker worker to build
Update npm to latest version for each Node.js
Merge branch 'master' of github.com:travis-ci/travis-cookbooks
Update ElasticSearch to 1.3.4
Link all binaries created by ElasticSearch debian package
Create symbolic links with a ruby_block
Use File.symlink instead

`#link` is not defined here
Fix elasticsearch symlinking
PHP updates
Merge pull request #394 from GrahamCampbell/php

PHP Updates
Use special PPA only for Precise

For Trusty, there is a package from
http://packages.ubuntu.com/trusty/libzmq3

Fixes https://github.com/travis-ci/travis-ci/issues/2558
Undo enable-dynamic-scripting for elasticsearch

According to https://github.com/travis-ci/travis-ci/issues/2884,
dynamic scripting is on by default with ES 1.3.4
Update nvm to v0.17.3