Simplify ceilometer-api and checks Keystone middleware parsing

This adds some test to be sure options passed to the middleware are read and
user properly.

This fixes bug #1099739

Change-Id: I491db4d2c7387cc2848ebefbbb579597234a82b0
Signed-off-by: Julien Danjou <julien@danjou.info>
Merge "Simplify ceilometer-api and checks Keystone middleware parsing"