Restructured and updated Neutron compute section

As part of the installation guide improvement project, I performed
the following operations on the Neutron compute section:

1) Removed modularity since we will only support the ML2 plug-in
   for Icehouse.
2) Added some <procedure> tags to separate content. Future patches
   will add descriptions of each procedure.
3) Unified indentation and spacing.
4) Removed database configuration steps since Icehouse uses AMQP on
   compute nodes.
5) Removed *.ini configuration steps since Icehouse doesn't require
   editing *.ini files.
6) Moved 'auth_uri' key under [keystone_authtoken] section in
   neutron.conf.
7) Removed defunct 'auth_url' key.

This section should continue to work for installations using the Open
vSwitch plug-in for Neutron. Future patches will update the content
to use ML2.

Change-Id: I2c6207b26a8f85078ac680110d3d3244e8affd75
Partial-Bug: #1291071
Implements: blueprint networking-install-guide-improvements
Merge "Restructured and updated Neutron compute section"