keep scope query within x-shard block
keep scope query within x-shard block

closes FOO-1126

TEST PLAN:
  1) try to import a user that has more than 100
     paths with the same email address
  2) SIS import should not bomb

Change-Id: I642ea259accdc3b50060f9f28a803211f026830e
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/251650
Tested-by: Ethan Vizitei <73eeb0b2f65d05a906adf3b21ee1f9f5a2aa3c1c@instructure.com>
Reviewed-by: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
QA-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>
Product-Review: Rob Orton <7e09c9d3e96378bf549fc283fd6e1e5b7014cc33@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms