Properly wait the slave to sync with master in BRPOPLPUSH test.

tests/integration/replication.tcl

@@ -2,9 +2,13 @@ start_server {tags {"repl"}} {
     start_server {} {
         test {First server should have role slave after SLAVEOF} {
             r -1 slaveof [srv 0 host] [srv 0 port]
-            after 1000
-            s -1 role
-        } {slave}
+            wait_for_condition 50 100 {
+                [s -1 role] eq {slave} &&
+                [string match {*master_link_status:up*} [r -1 info replication]]
+            } else {
+                fail "Can't turn the instance into a slave"
+            }
+        }
 
         test {BRPOPLPUSH replication, when blocking against empty list} {
             set rd [redis_deferring_client]