Add missing unique constraint to KeyPair model.

Added a missing unique constraint ("name", "user_id") to KeyPair model
(this constraint was in db schema but not in model definition).

blueprint db-enforce-unique-keys

Change-Id: Id231bca256e0cb39fcd8068acc7039240326fde2
Merge "Add missing unique constraint to KeyPair model."
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp