Add info about uninstalling OpenStack

Sometimes you have to uninstall OpenStack the hard way.
This additional section explains how.

Also fixed a bug where the 'upgrades' section was at the wrong
level in the nesting tree.

fixes bug 1040046

Change-Id: Id9063b118270129e2dbcab79909fc4549a16d37b
Merge "Add info about uninstalling OpenStack"