SPARK-2486: Utils.getCallSite is now resilient to bogus frames

When running Spark under certain instrumenting profilers,
Utils.getCallSite could crash with an NPE.  This commit
makes it more resilient to failures occurring while inspecting
stack frames.

Author: William Benton <willb@redhat.com>

Closes #1413 from willb/spark-2486 and squashes the following commits:

b7c0274 [William Benton] Use explicit null checks instead of Try()
0f0c1ae [William Benton] Utils.getCallSite is now resilient to bogus frames

core/src/main/scala/org/apache/spark/util/Utils.scala

@@ -809,7 +809,11 @@ private[spark] object Utils extends Logging {
    */
   def getCallSite: CallSite = {
     val trace = Thread.currentThread.getStackTrace()
-      .filterNot(_.getMethodName.contains("getStackTrace"))
+      .filterNot((ste:StackTraceElement) => 
+        // When running under some profilers, the current stack trace might contain some bogus 
+        // frames. This is intended to ensure that we don't crash in these situations by
+        // ignoring any frames that we can't examine.
+        (ste == null || ste.getMethodName == null || ste.getMethodName.contains("getStackTrace")))
 
     // Keep crawling up the stack trace until we find the first function not inside of the spark
     // package. We track the last (shallowest) contiguous Spark method. This might be an RDD