Fix inefficiency in getBridgelessNetworks

This commit makes getBridgelessNetworks use the Netinfo instance
networks instead of generating its own. Additionally, it is put in
the style and vicinity of the most semantically similar method of
the class, to improve the module's readability.

Change-Id: I68b5ecf415d4ab49a56019d8875dde57ca29d1fc
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/11071
Reviewed-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>