Add package_manifest resource.

Add package_manifest resource.

This patch converts the write_package_names function into
a proper resource. Using the write_package_names only works
if the function comes last in the puppet manifest. By
making the same functionality a custom resource we allow
for it to exist anywhere in the manifest and provide the
same functionality.

 The new syntax would be:

 package_manifest{'/tmp/foo': ensure => present}

Co-Authored-By: Martin Mágr <mmagr@redhat.com>
Change-Id: If3e03b1983fed47082fac8ce63f975557dbc503c