[SPARK-11134] [core] Increase LauncherBackendSuite timeout.

[vanzin]

This test can take a little while to finish on slow / loaded machines.

[SparkQA]

Test build #44184 has finished for PR 9235 at commit b265ec2.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):\n * case class LongEncoder(fieldName: String = \"value\", ordinal: Int = 0) extends Encoder[Long]\n * case class IntEncoder(fieldName: String = \"value\", ordinal: Int = 0) extends Encoder[Int]\n * case class StringEncoder(\n * |class Tuple$\n * class Tuple2Encoder[T1, T2](e1: Encoder[T1], e2: Encoder[T2]) extends Encoder[(T1, T2)]\n * class Tuple3Encoder[T1, T2, T3](e1: Encoder[T1], e2: Encoder[T2], e3: Encoder[T3]) extends Encoder[(T1, T2, T3)]\n * class Tuple4Encoder[T1, T2, T3, T4](e1: Encoder[T1], e2: Encoder[T2], e3: Encoder[T3], e4: Encoder[T4]) extends Encoder[(T1, T2, T3, T4)]\n * class Tuple5Encoder[T1, T2, T3, T4, T5](e1: Encoder[T1], e2: Encoder[T2], e3: Encoder[T3], e4: Encoder[T4], e5: Encoder[T5]) extends Encoder[(T1, T2, T3, T4, T5)]\n * implicit class AttributeSeq(attrs: Seq[Attribute])\n * case class MapPartitions[T, U](\n * case class AppendColumn[T, U](\n * case class MapGroups[K, T, U](\n * class TypedColumn[T](expr: Expression)(implicit val encoder: Encoder[T]) extends Column(expr)\n * abstract class SQLImplicits\n * case class MapPartitions[T, U](\n * case class AppendColumns[T, U](\n * case class MapGroups[K, T, U](\n

[rxin]

I've merged this. Thanks.