Raising 400 Bad Request when using "changes-since" filter on v2

In Glance API V2, currently, the user gets a 500 error when tries
to use the "changes-since" filter.This filter, which was available
on API v1 is no longer available on V2.

This patch returns to the user a 400 Bad Request with a proper message,
instead of a generic 500 Internal Server Error.

Change-Id: Icece859a7f12f6f4aa1f7bb945134a935048b315
Closes-bug: 1273975
Refactoring Glance logging lowering levels

This change fixes translations to be using correct translation functions.
Contains few log level drops for too high logging levels.

This PS does not address logging changes for modules under glance/store/
due to the new repo request. After stores are moved to their own repo
new PS will be submitted for those.

This PS does not touch the test code.

Separate PS will be submitted for log lever raises withing codebase
as requested during the spec review.

Related to bp refactoring-glance-logging

Change-Id: I683c35face8d5b7056ef7fedcd75deb63dbbf8e2
Merge "Raising 400 Bad Request when using "changes-since" filter on v2"
Merge "Refactoring Glance logging lowering levels"