Bump MODULE_VERSION to 5.2.1

Change-Id: I111d9902592255ee41a665b5b34e14f4885e9136
Reviewed-by: Matti Paaso <matti.paaso@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Merge remote-tracking branch 'origin/release' into stable

Change-Id: I49876f1e23dc0506d8ff4df5341540fef6095dc2