Update keystone content for Juno

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

1) Added step to manually create '_member_' role because
   source/package no longer creates it automatically.
2) Removed defunct 'log_dir' workaround for Ubuntu.
3) Explicitly created endpoint with 'regionOne' region to avoid
   inconsistent defaults.
4) Recommended enabling verbose logging.
5) Removed prompts specific to MySQL because most distributions
   will use MariaDB.
6) Improved consistency with similar content from other services
   as approved with the installation guide improvements project.

Change-Id: I46a95f9a29bfab4da9961d2393f33ff65c46aec4
Merge "Update keystone content for Juno"