new module to handle FreeBSD packages with pkgng

New binary package management should be the default soon in FreeBSD, and
is already fully useable through self generated and non official binary
repositories.

- add support for pkgng
- support specifying the repository url as a parameter
- allow not to update cache

Signed-off-by: bleader <bleader@ratonland.org>
Merge pull request #2883 from bleader/devel

new module to handle FreeBSD packages with pkgng