Use true() rather than variable/singleton

SqlAlchemy provides a true() factory so we don't have to work around
PEP8 issues with comparing singletons.

Change-Id: Icdff30d85beb068d10b987aea0e5a6e71098316a
Fix the copy-pasted help info for db_version

The previous help message was a simple copy-paste
from db_sync.

Change-Id: Ibf8f990ca130ee713c9fad2d1142e1657205ff8b
Closes-Bug: #1397207
Fixes docstring at eventlet_server

The WSGI server is a normal process (not a thread as being
described in the docstring), it uses a green thread pool though,
to handle upcoming jobs.

Change-Id: I688175eeaccd4c1aa4b2ee5564745b502b9cb748
Closes-Bug: 1380477
Multiple IdPs problem

The documentation is modified in order to allow mulitple
IdPs using the OS-Federation avoiding conflicts among them.

The previous proposed configuration allows user from one IdP
to get mapped as user from a different IdP. With the chenge
proposed this is not anymore possible.

Change-Id: I9d62a840c122fb36c02c56a84c4f2ef8c30303c4
Closes-Bug: 1390124
Merge "Fixes docstring at eventlet_server"
Merge "Fix the copy-pasted help info for db_version"
Merge "Use true() rather than variable/singleton"