update test_conv to cover Nones in input shape
update test_conv to cover Nones in input shape

ebattenberg/Lasagne,DeanChan/Lasagne,kracwarlock/Lasagne,Richi91/nntools,cancan101/Lasagne,DataFighter/Lasagne-tutorial,mheilman/Lasagne,takacsg84/Lasagne,ErnstHowie/Lasagne,gabortakacs/Lasagne,MihailoIsakov/fishfish,dnuffer/Lasagne,rlkelly/Lasagne