Bug 856665

Description of problem:
Copied from 
https://github.com/Katello/katello/pull/615#issuecomment-8491564

Adding keys for *_id columns are quite obvious. But please spend time on /var/log/katello/production_sql.log with 
KATELLO_LOGGING_SQL=debug
and with some data in db.

I investigated some random slow queries and find that katello can utilize indexes:

help_tips (key, user_id);
environments ( organization_id, library)
organizations (cp_key, task_id)
task_statuses (uuid, type)
verb (verb)
environment_priors (prior_id, environment_id)
And for example index
environment_priors (prior_id, environment_id)
can be used instead of 
environment_priors (prior_id)
so such simple index is not really needed.

Also it would be very usefull to add each index in separate commit, with explanation which SQL query it is addressing so we can see, it is actually doing something. For example:

Adding index:
  verb (verb)

addressing:
SELECT "verbs".* FROM "verbs" WHERE "verbs"."verb" = 'register_systems' LIMIT 1
or

Adding index:
  environment_priors (prior_id, environment_id)

addressing:
  SELECT "environments".* FROM "environ