[KYUUBI #1379] Make SESSION_ENGINE_LAUNCH_ASYNC true by default

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### _How was this patch tested?_
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Closes #1379 from turboFei/async_open_default.

Closes #1379

a7c4c6a [Fei Wang] fix ut
cc8d273 [Fei Wang] Make SESSION_ENGINE_LAUNCH_ASYNC true by default

Authored-by: Fei Wang <fwang12@ebay.com>
Signed-off-by: Fei Wang <fwang12@ebay.com>

Author: turboFei

docs/deployment/settings.md

@@ -300,7 +300,7 @@ kyuubi\.session\.conf<br>\.restrict\.list|<div style='width: 65pt;word-wrap: bre
 kyuubi\.session\.engine<br>\.check\.interval|<div style='width: 65pt;word-wrap: break-word;white-space: normal'>PT5M</div>|<div style='width: 170pt;word-wrap: break-word;white-space: normal'>The check interval for engine timeout</div>|<div style='width: 30pt'>duration</div>|<div style='width: 20pt'>1.0.0</div>
 kyuubi\.session\.engine<br>\.idle\.timeout|<div style='width: 65pt;word-wrap: break-word;white-space: normal'>PT30M</div>|<div style='width: 170pt;word-wrap: break-word;white-space: normal'>engine timeout, the engine will self-terminate when it's not accessed for this duration. 0 or negative means not to self-terminate.</div>|<div style='width: 30pt'>duration</div>|<div style='width: 20pt'>1.0.0</div>
 kyuubi\.session\.engine<br>\.initialize\.timeout|<div style='width: 65pt;word-wrap: break-word;white-space: normal'>PT3M</div>|<div style='width: 170pt;word-wrap: break-word;white-space: normal'>Timeout for starting the background engine, e.g. SparkSQLEngine.</div>|<div style='width: 30pt'>duration</div>|<div style='width: 20pt'>1.0.0</div>
-kyuubi\.session\.engine<br>\.launch\.async|<div style='width: 65pt;word-wrap: break-word;white-space: normal'>false</div>|<div style='width: 170pt;word-wrap: break-word;white-space: normal'>When opening kyuubi session, whether to launch backend engine asynchronously. When true, the Kyuubi server will set up the connection with the client without delay as the backend engine will be created asynchronously.</div>|<div style='width: 30pt'>boolean</div>|<div style='width: 20pt'>1.4.0</div>
+kyuubi\.session\.engine<br>\.launch\.async|<div style='width: 65pt;word-wrap: break-word;white-space: normal'>true</div>|<div style='width: 170pt;word-wrap: break-word;white-space: normal'>When opening kyuubi session, whether to launch backend engine asynchronously. When true, the Kyuubi server will set up the connection with the client without delay as the backend engine will be created asynchronously.</div>|<div style='width: 30pt'>boolean</div>|<div style='width: 20pt'>1.4.0</div>
 kyuubi\.session\.engine<br>\.log\.timeout|<div style='width: 65pt;word-wrap: break-word;white-space: normal'>PT24H</div>|<div style='width: 170pt;word-wrap: break-word;white-space: normal'>If we use Spark as the engine then the session submit log is the console output of spark-submit. We will retain the session submit log until over the config value.</div>|<div style='width: 30pt'>duration</div>|<div style='width: 20pt'>1.1.0</div>
 kyuubi\.session\.engine<br>\.login\.timeout|<div style='width: 65pt;word-wrap: break-word;white-space: normal'>PT15S</div>|<div style='width: 170pt;word-wrap: break-word;white-space: normal'>The timeout of creating the connection to remote sql query engine</div>|<div style='width: 30pt'>duration</div>|<div style='width: 20pt'>1.0.0</div>
 kyuubi\.session\.engine<br>\.request\.timeout|<div style='width: 65pt;word-wrap: break-word;white-space: normal'>PT1M</div>|<div style='width: 170pt;word-wrap: break-word;white-space: normal'>The timeout of awaiting response after sending request to remote sql query engine</div>|<div style='width: 30pt'>duration</div>|<div style='width: 20pt'>1.4.0</div>

kyuubi-common/src/main/scala/org/apache/kyuubi/config/KyuubiConf.scala

@@ -664,15 +664,14 @@ object KyuubiConf {
       .checkValue(_ > 0, "the maximum must be positive integer.")
       .createWithDefault(10)
 
-  // TODO: make it true by default
   val SESSION_ENGINE_LAUNCH_ASYNC: ConfigEntry[Boolean] =
     buildConf("session.engine.launch.async")
       .doc("When opening kyuubi session, whether to launch backend engine asynchronously." +
         " When true, the Kyuubi server will set up the connection with the client without delay" +
         " as the backend engine will be created asynchronously.")
       .version("1.4.0")
       .booleanConf
-      .createWithDefault(false)
+      .createWithDefault(true)
 
   val SERVER_EXEC_POOL_SIZE: ConfigEntry[Int] =
     buildConf("backend.server.exec.pool.size")

kyuubi-server/src/test/scala/org/apache/kyuubi/operation/KyuubiOperationPerConnectionSuite.scala

@@ -57,7 +57,9 @@ class KyuubiOperationPerConnectionSuite extends WithKyuubiServer with HiveJDBCTe
   }
 
   test("submit spark app timeout with last log output") {
-    withSessionConf()(Map(KyuubiConf.ENGINE_INIT_TIMEOUT.key -> "2000"))(Map.empty) {
+    withSessionConf()(Map(
+      KyuubiConf.ENGINE_INIT_TIMEOUT.key -> "2000",
+      KyuubiConf.SESSION_ENGINE_LAUNCH_ASYNC.key -> "false"))(Map.empty) {
       val exception = intercept[SQLException] {
         withJdbcStatement() { _ => // no-op
         }