Update run_list for standard VM

**Changes:** 

- PostgreSQL recipe name has changed after travis-ci/travis-cookbooks#221
- MySQL client recipe is included by server recipe
- No more needed to override PostgreSQL max_connections attribute
- No need to override MySQL server_root_password attribute

**Related Notes:**

- Why not directly set `default[:travis_build_environment][:use_tmpfs_for_builds] = false` in travis-cookbooks ?
- I've not verified yet the overrides of `rvm` cookbook...