Update neutron content for Juno

I updated neutron content in the installation guide for Juno
as follows:

1) Renamed files and IDs since the guide no longer needs to
   differentiate between the ML2 and OVS plug-ins.
2) Removed prompts specific to MySQL because most distributions
   will use MariaDB.
3) Explicitly created endpoint with 'regionOne' region to avoid
   inconsistent defaults.
4) Replaced 'auth_*' options with 'identity_uri' option.
5) Moved neutron configuration options to [neutron] section in
   nova.conf.
6) Recommended enabling verbose logging.
7) Removed workarounds for Ubuntu 12.04.
8) Removed note about CirrOS lacking support for the DHCP MTU
   option.
9) Explicitly defined flat external network type.
10) Added example command output and updated existing command
    output.
11) Added and updated glossary terms.
12) Implemented changes from the improvements blueprint including
    structure and phrasing.

Change-Id: I13baa94585bb6e8b22d8d79043fc84cbc2514954
Implements: blueprint installation-guide-improvements
Merge "Update neutron content for Juno"