Decision Tree: Add unit test for checking the variable names in the returned type of c45_train/rf_train
Decision Tree: Add unit test for checking the variable names in the returned type of c45_train/rf_train

Jira: MADLIB-633

There were no unit tests for checking the returned type.  It would be better if we have
the checking so that we can find the changes during development.

lmatthieu/incubator-madlib,rvs/incubator-madlib,orhankislal/incubator-madlib,hpandeycodeit/incubator-madlib,iyerr3/incubator-madlib,hpandeycodeit/incubator-madlib,cooper-sloan/incubator-madlib,apache/incubator-madlib,orhankislal/madlib,hpandeycodeit/incubator-madlib,madlib/madlib,lmatthieu/incubator-madlib,njayaram2/incubator-madlib,orhankislal/madlib,rashmi815/incubator-madlib,njayaram2/madlib,rvs/incubator-madlib,orhankislal/madlib,lmatthieu/incubator-madlib,orhankislal/incubator-madlib,cooper-sloan/incubator-madlib,hpandeycodeit/incubator-madlib,njayaram2/incubator-madlib,cooper-sloan/incubator-madlib,apache/incubator-madlib,rashmi815/incubator-madlib,njayaram2/madlib,mktal/incubator-madlib,njayaram2/madlib,madlib/madlib,iyerr3/incubator-madlib,cooper-sloan/incubator-madlib,iyerr3/incubator-madlib,apache/incubator-madlib,njayaram2/incubator-madlib,madlib/madlib,rvs/incubator-madlib,rvs/incubator-madlib,cooper-sloan/incubator-madlib,njayaram2/madlib,orhankislal/incubator-madlib,apache/incubator-madlib,lmatthieu/incubator-madlib,mktal/incubator-madlib,njayaram2/madlib,mktal/incubator-madlib,iyerr3/incubator-madlib,iyerr3/incubator-madlib,lmatthieu/incubator-madlib,rvs/incubator-madlib,njayaram2/incubator-madlib,madlib/madlib,mktal/incubator-madlib,madlib/madlib,orhankislal/incubator-madlib,njayaram2/incubator-madlib,orhankislal/madlib,hpandeycodeit/incubator-madlib,orhankislal/incubator-madlib,orhankislal/madlib,rashmi815/incubator-madlib,rashmi815/incubator-madlib,apache/incubator-madlib,mktal/incubator-madlib,rashmi815/incubator-madlib