Revert "extracted job template rendering into bosh-director-core gem"

While there was nothing wrong with the extraction, a bug in Rubygems 1.8
prevents us from successfully building a functioning stemcell. We will
have to sort that out before we bring this commit back.

This reverts commit a3f9159ada52d7a381a1820055a871f4f3f5438b.

Conflicts:
	Gemfile.lock