add conflicts/replaces to prevent double install
add postinst and postrm from puppet-common

this means the omnibus package will now create the puppet user and make
sure everything is owned by it
puppet provisioning: run apt-get update before pkg install

when i booted a vagrant server i'd consistently get package install
failures. running an apt-get update first flushes them out.

also spruce up the puppet code so it passes lint.
bump to latest minor version of puppet 2.7
bump factor to 1.7.4, rev 2 of omnibus pkg