(PUP-3227) Address man page ownship conflicts

Prior to this commit, upgrading from puppet=2.7.23-1~deb7u3 and
puppetmaster=2.7.23-1~deb7u3 to puppet=3.7.0.29-1puppetlabs1 and
puppetmaster=3.7.0.29-1puppetlabs1 fails. I believe this problem is due
to how Debian chose to package puppet-common, which owns
/usr/share/man/man8/puppet-master.8.gz.

This commit adds in a Conflicts: to the puppetmaster and
puppetmaster-common packages to make sure that we can successfully
upgrade from these older package versions. However, if a user has
puppetmaster and puppet older than 3.3.0 installed on a machine, and
only upgrades puppetmaster, this will uninstall the puppet package from
the system.