Improve install guide openrc content

Improve openrc content in the installation guide as follows:

1) Add new openrc section to keystone chapter
2) Remove clients chapter

This patch implements changes approved for other patches associated
with this blueprint.

Change-Id: I075671cb0b432ce73addb972a0d709f9a4655114
Implements: blueprint installation-guide-improvements
Merge "Improve install guide openrc content"