Updated networking content

I updated the networking content as follows:

1) Reordered example architectures to place the 3-node neutron
   architecture before the 2-node nova-network architecture which
   agrees with the order presented in other portions of the
   installation guide.
2) Changed network service naming to agree with conventions.
3) Permanently unlinked the Open vSwitch (OVS) plug-in sections from
   the Networking chapter. However, I will refrain from deleting
   the associated files in case we need to restore them.
4) Temporarily unlinked the Open vSwitch (OVS) portion of the Neutron
   concepts section until we can update it to reflect the Modular
   Layer 2 (ML2) plug-in.
5) Addressed other minor issues.

Change-Id: I7c285fcabaab65237477e8241f406dac28190344
Closes-Bug: #1309636
Merge "Updated networking content"