[SPARK-16379][CORE][MESOS] Spark on mesos is broken due to race condition in Logging

## What changes were proposed in this pull request?

The commit 044971eca0 introduced a lazy val to simplify code in Logging. Simple enough, though one side effect is that accessing log now means grabbing the instance's lock. This in turn turned up a form of deadlock in the Mesos code. It was arguably a bit of a problem in how this code is structured, but, in any event the safest thing to do seems to be to revert the commit, and that's 90% of the change here; it's just not worth the risk of similar more subtle issues.

What I didn't revert here was the removal of this odd override of log in the Mesos code. In retrospect it might have been put in place at some stage as a defense against this type of problem. After all the Logging code still involved a lock at initialization before the change in question.

Even after the revert, it doesn't seem like it does anything, given how Logging works now, so I left it removed. However, I also removed the particular log message that ended up playing a part in this problem anyway, maybe being paranoid, to make sure this type of problem can't happen even with how the current locking works in logging initialization.

## How was this patch tested?

Jenkins tests

Author: Sean Owen <sowen@cloudera.com>

Closes #14069 from srowen/SPARK-16379.

core/src/main/scala/org/apache/spark/internal/Logging.scala

@@ -32,10 +32,7 @@ private[spark] trait Logging {
 
   // Make the log field transient so that objects with Logging can
   // be serialized and used on another machine
-  @transient lazy val log: Logger = {
-    initializeLogIfNecessary(false)
-    LoggerFactory.getLogger(logName)
-  }
+  @transient private var log_ : Logger = null
 
   // Method to get the logger name for this object
   protected def logName = {
@@ -43,6 +40,15 @@ private[spark] trait Logging {
     this.getClass.getName.stripSuffix("$")
   }
 
+  // Method to get or create the logger for this object
+  protected def log: Logger = {
+    if (log_ == null) {
+      initializeLogIfNecessary(false)
+      log_ = LoggerFactory.getLogger(logName)
+    }
+    log_
+  }
+
   // Log methods that take only a String
   protected def logInfo(msg: => String) {
     if (log.isInfoEnabled) log.info(msg)

core/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosCoarseGrainedSchedulerBackend.scala

@@ -244,7 +244,6 @@ private[spark] class MesosCoarseGrainedSchedulerBackend(
       d: org.apache.mesos.SchedulerDriver, frameworkId: FrameworkID, masterInfo: MasterInfo) {
     appId = frameworkId.getValue
     mesosExternalShuffleClient.foreach(_.init(appId))
-    logInfo("Registered as framework ID " + appId)
     markRegistered()
   }