Sync models with migrations

Fixed bugs:
- wrong type instead of MediumText (InstanceInfoCache, Instance, ComputeNode),
- skipped indexes (SecurityGroup, Instance),
- wrong length of column (ComputeNodeStat),
- wrong order of columns in index (KeyPair),
- missing name of UniwueConstraint (InstanceGroup).

bp: db-sync-models-with-migrations

Change-Id: Id698fabd553a10326d984f88fc9580d88cd2a22e
Merge "Sync models with migrations"