Ensure assertions in Graph.apply are asserted.

The Graph.apply test in GraphSuite had some assertions in a closure in
a graph transformation. As a consequence, these assertions never
actually executed.  Furthermore, these closures had a reference to
(non-serializable) test harness classes because they called assert(),
which could be a problem if we proactively check closure serializability
in the future.

This commit simply changes the Graph.apply test to collect the graph
triplets so it can assert about each triplet from a map method.

graphx/src/test/scala/org/apache/spark/graphx/GraphSuite.scala

@@ -62,7 +62,7 @@ class GraphSuite extends FunSuite with LocalSparkContext {
       assert( graph.edges.count() === rawEdges.size )
       // Vertices not explicitly provided but referenced by edges should be created automatically
       assert( graph.vertices.count() === 100)
-      graph.triplets.map { et =>
+      graph.triplets.collect.map { et =>
         assert((et.srcId < 10 && et.srcAttr) || (et.srcId >= 10 && !et.srcAttr))
         assert((et.dstId < 10 && et.dstAttr) || (et.dstId >= 10 && !et.dstAttr))
       }