(packaging) Update template task for new erb_file method

The packaging repo will have all utilities split out into different classes for
sanity's sake, and one of the tools that got an overhaul is erb. This commit
updates puppetdb to use the new utility.
(packaging) Update top-level Rakefile's version and pe determination

Prior to the commit, the versioning in puppetdb would fail from a rake
perspective if the packaging repo wasn't present. This commit updates it to
fall back to git describe and if that fails to a hardcoded string, so that we
always have a version. We also set the @version variable to
Pkg::Config.version, which is how we access data provided by the packaging repo
in the new library-format.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>