Update slave upstart script to read locale

Ensures when jobs are run they have a LANG env variable set from
/etc/default/locale
Merge pull request #4 from alphagov/slave_locale

Update slave upstart script to read locale
Don't supress final newline in exec line.

This was causing the 'end script' line to be wrapped up onto the end of
the previous line, which broke things
anchor init to allow external requires on Class[::jenkins]