Fix _getNetworkIp for non-bridged networks.

Since this method servers for any kind of network, not just
bridged ones, we shouldn't convert network to the backing
device before calling getaddr.

Bug-Url: https://bugzilla.redhat.com/921595
Change-Id: Ie63c783cfde43dee3e470e7eb4a8b1811833e52e
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/13136
Tested-by: Martin Pavlik <xpavli44@gmail.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>