Update installation guide for Juno release

I updated the installation guide for Juno release packages
on Ubuntu as follows:

1) Removed "debug" workaround for horizon.
2) Removed "sudoers" workaround for cinder.
3) Fixed other minor issues.

Change-Id: Ie4895ad4e339ca2cf860eee2203afea5d701b95c
Merge "Update installation guide for Juno release"