Remove useless/unused stuff around .bashrc files

- .bashrc of 'travis' user explicitly loaded /etc/profile
  definitions, but /etc/profile.d mechanism is applied by default in
  bash shell creation.
- .bashrc of 'root' user is managed with a template, not anymore with a
  cookbook file.
Merge pull request #154 from travis-ci/fix-path-envvar

Clean up around management of PATH environment variable