Required AM memory is "amMem", not "args.amMemory"

"ERROR yarn.Client: Required AM memory (1024) is above the max threshold (1048) of this cluster" appears if this code is not changed. obviously, 1024 is less than 1048, so change this

Author: derek ma <maji3@asiainfo-linkage.com>

Closes #1494 from maji2014/master and squashes the following commits:

b0f6640 [derek ma] Required AM memory is "amMem", not "args.amMemory"

yarn/common/src/main/scala/org/apache/spark/deploy/yarn/ClientBase.scala

@@ -109,7 +109,7 @@ trait ClientBase extends Logging {
     if (amMem > maxMem) {
 
       val errorMessage = "Required AM memory (%d) is above the max threshold (%d) of this cluster."
-        .format(args.amMemory, maxMem)
+        .format(amMem, maxMem)
       logError(errorMessage)
       throw new IllegalArgumentException(errorMessage)
     }