Filter Blue Box templates by 'pool'

Here, we introduce a new config parameter 'queue' in '.travis.yml'
which will optionally select which Blue Box template pool to select
the Blue Box template.

If there is no 'queue' in '.travis.yml', it behaves exactly the
same as before.

If there is, its value is used to match against the teamplates'
descriptions to find the templates which have the value (as a word)
in them.

For example, if we have a job with 'queue: update' in '.travis.yml',
we will choose a tamplate from the pool of templates that have the
descriptions of the form

  /^travis-update-([\w-]+)-\d{4}-\d{2}-\d{2}-\d{2}-\d{2}/

If no such template exists, we fall back to the current rule to
find
  /^travis-([\w-]+)-\d{4}-\d{2}-\d{2}-\d{2}-\d{2}/
Update Gemfile.lock
Add second parameter in Blue Box image selection

Second parameter is now required to choose a non-production image
on Blue Box.

Following the suggestion made in https://github.com/travis-pro/ops/issues/326#issuecomment-52304661
we now look for images with the name of the form: travis-DIST-GROUP-TEMPLATE-%Y-%m-%d-%H-%M-SHA1
where `DIST` is specified in .travis.yml with the top-level `dist`,
`GROUP` with `group`, and `TEMPLATE` with `language`.
Merge branch 'ha-feature-template_group_selection' of github.com:travis-ci/travis-worker into ha-feature-template_group_selection
Tweak Regexp to match image name

The language name should consist of at most 2 words delimited
by a hyphen.