Wait for the role change and fix the timing issue in the new test (va…

…lkey-io#947)

The test might be fast enough and then there is no change in the role
causing the test to fail. Adding a wait to avoid the timing issue:
```
*** [err]: valkey-cli make source node ignores NOREPLICAS error when doing the last CLUSTER SETSLOT
Expected '{127.0.0.1 23154 267}' to be equal to '' (context: type eval line 24 cmd {assert_equal [lindex [R 3 role] 2] {}} proc ::test)
```

Signed-off-by: Binbin <[email protected]>
Signed-off-by: Ping Xie <[email protected]>

tests/unit/cluster/replica-migration.tcl

@@ -164,6 +164,7 @@ start_cluster 4 4 {tags {external:skip cluster} overrides {cluster-node-timeout
         R 7 config set cluster-allow-replica-migration yes
 
         # Record the current primary node, server 7 will be migrated later.
+        set old_role_response [R 7 role]
         set old_primary_ip [lindex [R 7 role] 1]
         set old_primary_port [lindex [R 7 role] 2]
 
@@ -177,6 +178,15 @@ start_cluster 4 4 {tags {external:skip cluster} overrides {cluster-node-timeout
             fail "valkey-cli --cluster rebalance returns non-zero exit code, output below:\n$result"
         }
 
+        # Wait for server 7 role response to change.
+        wait_for_condition 1000 50 {
+            [R 7 role] ne $old_role_response
+        } else {
+            puts "R 3 role: [R 3 role]"
+            puts "R 7 role: [R 7 role]"
+            fail "Server 7 role response has not changed"
+        }
+
         wait_for_cluster_propagation
         wait_for_cluster_state "ok"