[SPARK-4158] Fix for missing resources.

Mesos offers may not contain all resources, and Spark needs to check to
ensure they are present and sufficient.  Spark may throw an erroneous
exception when resources aren't present.

Author: brndnmtthws

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

@@ -242,8 +242,7 @@ private[spark] class CoarseMesosSchedulerBackend(
     for (r <- res if r.getName == name) {
       return r.getScalar.getValue
     }
-    // If we reached here, no resource with the required name was present
-    throw new IllegalArgumentException("No resource called " + name + " in " + res)
+    0
   }
 
   /** Build a Mesos resource protobuf object */

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

@@ -278,8 +278,7 @@ private[spark] class MesosSchedulerBackend(
     for (r <- res if r.getName == name) {
       return r.getScalar.getValue
     }
-    // If we reached here, no resource with the required name was present
-    throw new IllegalArgumentException("No resource called " + name + " in " + res)
+    0
   }
 
   /** Turn a Spark TaskDescription into a Mesos task */