In SafeLogging, make the log transient (apache-spark-on-k8s#471)

### Upstream SPARK-XXXXX ticket and PR link (if not applicable, explain)
No upstream PR - SafeLogging is palantir specific.

### What changes were proposed in this pull request?
If the log in SafeLogging is not marked as transient, it is included in the serialized version of TorrentBroadcast, which causes issues. This excludes the log from being included in the TorrentBroadcast object, by making the log transient.

### How was this patch tested?
No testing for this - the logic is taken from upstream

Author: vinooganesh

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

@@ -18,51 +18,66 @@
 package org.apache.spark.internal
 
 import com.palantir.logsafe.Arg
-import org.slf4j.LoggerFactory
+import org.slf4j.{Logger, LoggerFactory}
 
 trait SafeLogging {
-  private[this] val log_ = LoggerFactory.getLogger(this.getClass.getName)
+  // Taken from Logging.scala
+  @transient private[this] var safeLog_ : Logger = null
 
-  def safeLogIsInfoEnabled: Boolean = log_.isInfoEnabled
+  // Method to get the logger name for this object
+  protected def getLogName: String = {
+    // Ignore trailing $'s in the class names for Scala objects
+    this.getClass.getName.stripSuffix("$")
+  }
+
+  // Method to get or create the logger for this object
+  protected def safeLog: Logger = {
+    if (safeLog_ == null) {
+      safeLog_ = LoggerFactory.getLogger(getLogName)
+    }
+    safeLog_
+  }
+
+  def safeLogIsInfoEnabled: Boolean = safeLog.isInfoEnabled
 
   def safeLogInfo(message: String, args: Arg[_]*): Unit = {
-    if (log_.isInfoEnabled) log_.info(message, args: _*)
+    if (safeLog.isInfoEnabled) safeLog.info(message, args: _*)
   }
 
   def safeLogInfo(message: String, error: Throwable, args: Arg[_]*): Unit = {
-    if (log_.isInfoEnabled) log_.info(message, args :+ error: _*)
+    if (safeLog.isInfoEnabled) safeLog.info(message, args :+ error: _*)
   }
 
   def safeLogDebug(message: String, args: Arg[_]*): Unit = {
-    if (log_.isDebugEnabled) log_.debug(message, args: _*)
+    if (safeLog.isDebugEnabled) safeLog.debug(message, args: _*)
   }
 
   def safeLogDebug(message: String, error: Throwable, args: Arg[_]*): Unit = {
-    if (log_.isDebugEnabled) log_.debug(message, args :+ error: _*)
+    if (safeLog.isDebugEnabled) safeLog.debug(message, args :+ error: _*)
   }
 
   def safeLogTrace(message: String, args: Arg[_]*): Unit = {
-    if (log_.isTraceEnabled) log_.trace(message, args: _*)
+    if (safeLog.isTraceEnabled) safeLog.trace(message, args: _*)
   }
 
   def safeLogTrace(message: String, error: Throwable, args: Arg[_]*): Unit = {
-    if (log_.isTraceEnabled) log_.trace(message, args :+ error: _*)
+    if (safeLog.isTraceEnabled) safeLog.trace(message, args :+ error: _*)
   }
 
   def safeLogWarning(message: String, args: Arg[_]*): Unit = {
-    if (log_.isWarnEnabled) log_.warn(message, args: _*)
+    if (safeLog.isWarnEnabled) safeLog.warn(message, args: _*)
   }
 
   def safeLogWarning(message: String, error: Throwable, args: Arg[_]*): Unit = {
-    if (log_.isWarnEnabled) log_.warn(message, args :+ error: _*)
+    if (safeLog.isWarnEnabled) safeLog.warn(message, args :+ error: _*)
   }
 
   def safeLogError(message: String, args: Arg[_]*): Unit = {
-    if (log_.isErrorEnabled) log_.error(message, args: _*)
+    if (safeLog.isErrorEnabled) safeLog.error(message, args: _*)
   }
 
   def safeLogError(message: String, error: Throwable, args: Arg[_]*): Unit = {
-    if (log_.isErrorEnabled) log_.error(message, args :+ error: _*)
+    if (safeLog.isErrorEnabled) safeLog.error(message, args :+ error: _*)
   }
 }