Deflake atomic slot migration client flag test (#2720)

This test was failing, and causing the next test to throw an exception.
It is failing since we never waited for the slot migration to connect
before proceeding.

Fixes #2692

Signed-off-by: Jacob Murphy <[email protected]>
(cherry picked from commit 19474c8)
Signed-off-by: cherukum-amazon <[email protected]>

Author: murphyjacob4

tests/unit/cluster/cluster-migrateslots.tcl

@@ -568,6 +568,7 @@ start_cluster 3 3 {tags {logreqres:skip external:skip cluster} overrides {cluste
 
             assert_match "OK" [R 2 CLUSTER MIGRATESLOTS SLOTSRANGE 16383 16383 NODE $node0_id]
             set jobname [get_job_name 2 16383]
+            wait_for_migration_field 2 $jobname state waiting-to-pause
 
             # Check the flags
             verify_client_flag 0 "E" 0