[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: Brenden Matthews <brenden@diddyinc.com>

Closes #3024 from brndnmtthws/fix-mesos-resource-misuse and squashes the following commits:

e5f9580 [Brenden Matthews] [SPARK-4158] Fix for missing resources.

(cherry picked from commit cb0eae3)
Signed-off-by: Andrew Or <andrew@databricks.com>

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

@@ -235,8 +235,7 @@ 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

@@ -273,8 +273,7 @@ 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 */