It turned out that templates/base is used to create new plugin
directory structure by fpb --create and, therefore, is a bad place to
put Release.mako since it is attempted to render it at plugin creation
time, not at a build time as inteded.
Change-Id: I7dbbf192827f8b2a0c0675050f7b48820952f6af
Closes-Bug: #1655289