Neutron: fix missing add bridge step in provider router demo

The step to add the bridge that links the physical network
for the vlan provider networks was missing.

Also fixed a couple of minor mistakes on the same page.

Bug: 1221413
Change-Id: Ib022cb1895deea2da9e5bdfad182089597bb8f3b
Merge "Neutron: fix missing add bridge step in provider router demo"