Fixes two doc bugs with networking install and admin

- ensures network-admin/admin is redirected as people are finding it
- ensures ubuntu output has ovs install instruction

Change-Id: I22cafaae77e247d8cc2a3d01cd1bfb8320b6efb3
backport: havana
Closes-bug: 1248791
Closes-bug: 1258377
Merge "Fixes two doc bugs with networking install and admin"