[SPARK-11790][Streaming][Tests]Increase the connection timeout

[zsxwing]

Sometimes, EmbeddedZookeeper may need more than 6 seconds to setup up in a slow Jenkins worker. So just increase the timeout, it won't increase the test time if the test passes.

[SparkQA]

Test build #46114 has finished for PR 9778 at commit 01ee569.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * class HashingTF(override val uid: String)\n * class Interaction @Since(\"1.6.0\") (override val uid: String) extends Transformer\n * class Normalizer(override val uid: String)\n * class SQLTransformer @Since(\"1.6.0\") (override val uid: String) extends Transformer with Writable\n * class Tokenizer(override val uid: String)\n * case class ArrayConversion(elementConversion: JDBCConversion) extends JDBCConversion\n * abstract class JdbcDialect extends Serializable\n

[andrewor14]

OK