Fix markup of app_demo_routers_with_private_networks.xml

My changes are mainly:
* use userinput instead of computeroutput as appropriate
* add prompts
* use programlisting (language="bash" only used for bash code)
* use filename

I also followed Diane's editorial suggestion rewording the initial
setup description.

Change-Id: I9bb53a93336e599dcd9d9426d7d821daf569611a
Thorough edit of the 'Using OpenStack Networking' chapter.

Moved long pages of commands into tables. Corrected grammatical errors, and added descriptive

Change-Id: I313c9704a0e2fcd5296c0ab26084ca81b774c6db
Merge "Fix markup of app_demo_routers_with_private_networks.xml"
Merge "Thorough edit of the 'Using OpenStack Networking' chapter."