Depend on puppet-common, not puppet

...as the puppet package configures the puppet agent to autostart (as of
trusty, at any rate).
puppet-git-receiver (1.5.1+nmu1) UNRELEASED; urgency=medium
Merge branch 'ppa-base' into series/trusty

* ppa-base:
  puppet-git-receiver (1.5.1+nmu1) UNRELEASED; urgency=medium
  Depend on puppet-common, not puppet
puppet-git-receiver (1.5.1+nmu1~14.04~ppa1) trusty; urgency=medium