Update basic environment content for Juno

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

1) Collapsed database section because it only includes procedures
   for the controller. Although the diagrams show the database on
   the controller node, I added some text to remind users.
2) Reorganized sections to improve flow. For example, moving the
   security section closer to the beginning of the chapter.

Change-Id: Icd43c2530982d356067c8a77ba4a744a2c63e0e4
Merge "Update basic environment content for Juno"