libnm is too new and is not in all of the distros that we still
support (eg: ubuntu 14.04). We can use libnm-glib instead. libnm
is just an API improvement to libnm-glib; since we don't use many
features of this library almost no changes are required in the code.

Change-Id: Ic40e7e26a91b91f3d104c68e8f60e945f1731fc3
Tuleap: #845