sql.Driver:authenticate() signatures should match

A method called authenticate_user was renamed in
identity.backends.sql.Driver from authenticate_user
to authenticate but the base class wasn't updated.

Also, the user_id and password arguments to authenticate
should NOT be optional.

Change-Id: Ie6eb42f060e368ec99d5d8241a404cf7c70d48ae
Ec2 credentials table not created during testing

This change makes it so that the SQL Ec2Credential unit tests
can be run individually. It does this by making sure the
credential table model is available before the tables are
created.

Before this change, you couldn't run these tests individually
and would get an error that the ec2_credential table doesn't
exist.

Part of fix for bug 1179259

Change-Id: I68c8b91b18ac0065628c979e5bcc56152ae14916
Load backends before deploy app in client tests

The backends should be loaded before the app is deployed for
the client tests, otherwise the wrong backends may be loaded
when the app is deployed.

Part of fix for bug 1204605

Change-Id: I70680c3daea3a863bcbde07b1ee7e062cd150e51
Merge "sql.Driver:authenticate() signatures should match"
Merge "Ec2 credentials table not created during testing"
Merge "Load backends before deploy app in client tests"