fix small test suite race conditions

tests/support/util.tcl

@@ -91,6 +91,14 @@ proc wait_for_sync r {
     }
 }
 
+proc wait_for_ofs_sync {r1 r2} {
+    wait_for_condition 50 100 {
+        [status $r1 master_repl_offset] eq [status $r2 master_repl_offset]
+    } else {
+        fail "replica didn't sync in time"
+    }
+}
+
 # Random integer between 0 and max (excluded).
 proc randomInt {max} {
     expr {int(rand()*$max)}