[SPARK-25277][YARN] YARN applicationMaster metrics should not register static metrics

## What changes were proposed in this pull request?

YARN applicationMaster metrics registration introduced in SPARK-24594 causes further registration of static metrics (Codegenerator and HiveExternalCatalog) and of JVM metrics, which I believe do not belong in this context.
This looks like an unintended side effect of using the start method of [[MetricsSystem]].
A possible solution proposed here, is to introduce startNoRegisterSources to avoid these additional registrations of static sources and of JVM sources in the case of YARN applicationMaster metrics (this could be useful for other metrics that may be added in the future).

## How was this patch tested?

Manually tested on a YARN cluster,

Closes #22279 from LucaCanali/YarnMetricsRemoveExtraSourceRegistration.

Lead-authored-by: Luca Canali <luca.canali@cern.ch>
Co-authored-by: LucaCanali <luca.canali@cern.ch>
Signed-off-by: Marcelo Vanzin <vanzin@cloudera.com>

Author: LucaCanali

core/src/main/scala/org/apache/spark/metrics/MetricsSystem.scala

@@ -94,11 +94,13 @@ private[spark] class MetricsSystem private (
 
   metricsConfig.initialize()
 
-  def start() {
+  def start(registerStaticSources: Boolean = true) {
     require(!running, "Attempting to start a MetricsSystem that is already running")
     running = true
-    StaticSources.allSources.foreach(registerSource)
-    registerSources()
+    if (registerStaticSources) {
+      StaticSources.allSources.foreach(registerSource)
+      registerSources()
+    }
     registerSinks()
     sinks.foreach(_.start)
   }

resource-managers/yarn/src/main/scala/org/apache/spark/deploy/yarn/ApplicationMaster.scala

@@ -451,7 +451,8 @@ private[spark] class ApplicationMaster(args: ApplicationMasterArguments) extends
     val ms = MetricsSystem.createMetricsSystem("applicationMaster", sparkConf, securityMgr)
     val prefix = _sparkConf.get(YARN_METRICS_NAMESPACE).getOrElse(appId)
     ms.registerSource(new ApplicationMasterSource(prefix, allocator))
-    ms.start()
+    // do not register static sources in this case as per SPARK-25277
+    ms.start(false)
     metricsSystem = Some(ms)
     reporterThread = launchReporterThread()
   }