Add a pkg-map file so that Gentoo can avoid polluting the FS with
files not tracked in the package manager.
Changed the directory name so that the source-install method would
actually be disabled when DIB_INSTALLTYPE_pip_and_virtualenv=package
is set. Also changed source-repository line to be consistent with
the element name.
Change-Id: I5225bd7113ff2588c755ad4cd4ae9a2d78fff196
