integration_id validation added.
integration_id validation added.

If we try to create a user with the same id as an existing or remote user, we get the following error:

PG::UniqueViolation: ERROR:  duplicate key value violates unique constraint "index_pseudonyms_on_integration_id"
DETAIL:  Key (integration_id, account_id)=(0001, 1) already exists.

Adding this validation fixes this problem.

Closes gh-1285

Change-Id: I91621c22fb07bb991c1f62add282732f9fa3087f
Reviewed-on: https://gerrit.instructure.com/148729
Reviewed-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
QA-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Tested-by: Jenkins
Product-Review: Omar Khan <0cc1c8ba5d0ffa687b826700051767d448839fba@instructure.com>

sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms