Move various plugin configuration info from the old networking install chapter to Cloud Admin Guide

Move Big Switch, Nicira, OSV, PLUMgrid, Ryu, and neutron agent config info to ch_neworking
Add info about deleting nova-network before initializing networking install
Add crossreferences to Config Ref and Install Guide

author: nermina miller
backport: havana
Partial-Bug: 1244759

Change-Id: I5fe694de95da45879acccb5dfa45a331aa591403
Merge "Move various plugin configuration info from the old networking install chapter to Cloud Admin Guide"