Fixes DE216 - glance-registry-paste.ini password

[This could be separated into 2 commits]

The main organizational change here is removing the big chunk of code
from `glance::registry` that searches the node index for `glance::setup` to
find the db/admin passwords.  This unnecessarily duplicates
`RCB#get_settings_by_role`, which is called in `glance::common` anyway
(*BEFORE* this code even runs).  That's the first bug--the templates in
`glance::common` then try to use node values (set by this code) which
haven't been assigned yet.  So instead of fixing the ordering of the
code, just delete this unnecessary block and use the values discovered
by `get_settings_by_role()`.

The secondary changes are stylistic cleanup for readability and maint.