Sync models with migrations

This patch syncs models with migrations for:

-Endpoint
-CredentialModel
-TokenModel
-TrustModel

No actual schema change is taking place, this patch just corrects errors
in the model definitions.

Made class Index avaliable in keystone.common.sql.core

partially implements bp db-sync-models-with-migrations

Change-Id: I52f5c455360b65a2d5d884bbbec078dca6d34451
Merge "Sync models with migrations"