test/cluster/dtest: fix test_scrub_static_table flakiness

Pass jvm_args=["--smp", "1"] on both cluster.start() calls to
ensure consistent shard count across restarts, avoiding resharding
on restart. Also pass wait_for_binary_proto=True to cluster.start()
to ensure the CQL port is ready before connecting.

Fixes: SCYLLADB-824

Closes scylladb/scylladb#29548

(cherry picked from commit 34adb0e069)

Closes scylladb/scylladb#29557

test/cluster/dtest/scrub_test.py

@@ -236,7 +236,7 @@ class TestScrubIndexes(TestHelper):
                 "tablets_initial_scale_factor": 1,
             }
         )
-        cluster.populate(1).start(jvm_args=["--smp", "1"])
+        cluster.populate(1).start(jvm_args=["--smp", "1"], wait_for_binary_proto=True)
         node1 = cluster.nodelist()[0]
 
         session = self.patient_cql_connection(node1)
@@ -263,7 +263,7 @@ class TestScrubIndexes(TestHelper):
 
         # Restart and check data again
         cluster.stop()
-        cluster.start()
+        cluster.start(jvm_args=["--smp", "1"], wait_for_binary_proto=True)
 
         session = self.patient_cql_connection(node1)
         session.execute("USE %s" % (KEYSPACE))