[SPARK-19110][MLLIB][FOLLOWUP] Add a unit test for testing logPrior and logLikelihood of DistributedLDAModel in MLLIB

## What changes were proposed in this pull request?
#16491 added the fix to mllib and a unit test to ml. This followup PR, add unit tests to mllib suite.

## How was this patch tested?
Unit tests.

Author: wm624@hotmail.com <wm624@hotmail.com>

Closes #16524 from wangmiao1981/ldabug.

Author: wangmiao1981

mllib/src/test/scala/org/apache/spark/mllib/clustering/LDASuite.scala

@@ -505,6 +505,8 @@ class LDASuite extends SparkFunSuite with MLlibTestSparkContext {
       assert(distributedModel.topicConcentration === sameDistributedModel.topicConcentration)
       assert(distributedModel.gammaShape === sameDistributedModel.gammaShape)
       assert(distributedModel.globalTopicTotals === sameDistributedModel.globalTopicTotals)
+      assert(distributedModel.logLikelihood ~== sameDistributedModel.logLikelihood absTol 1e-6)
+      assert(distributedModel.logPrior ~== sameDistributedModel.logPrior absTol 1e-6)
 
       val graph = distributedModel.graph
       val sameGraph = sameDistributedModel.graph