netinfo: add bridge option reporting

This patch adds reporting of the bridge options that reside in
/sys/class/net/<bridge_name>/bridge/<opt_name>

Change-Id: I91ecc4bb652c5f676e62297aa3d6640bfee596fd
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/26749
Reviewed-by: Dan Kenigsberg <danken@redhat.com>