build: prevent CUDA_HOME KeyError (#316)
build: prevent CUDA_HOME KeyError (#316)

address: https://github.com/dmlc/MXNet.jl/issues/316#issuecomment-343660751
eric-haibin-lin/mxnet,ptrendx/mxnet,yajiedesign/mxnet,szha/mxnet,leezu/mxnet,tlby/mxnet,reminisce/mxnet,sxjscience/mxnet,leezu/mxnet,ptrendx/mxnet,dmlc/mxnet,reminisce/mxnet,sxjscience/mxnet,mbaijal/incubator-mxnet,dmlc/mxnet,reminisce/mxnet,DickJC123/mxnet,eric-haibin-lin/mxnet,larroy/mxnet,eric-haibin-lin/mxnet,leezu/mxnet,szha/mxnet,yajiedesign/mxnet,larroy/mxnet,tlby/mxnet,ptrendx/mxnet,ForkedReposBak/mxnet,mbaijal/incubator-mxnet,reminisce/mxnet,eric-haibin-lin/mxnet,mbaijal/incubator-mxnet,sxjscience/mxnet,leezu/mxnet,ptrendx/mxnet,ptrendx/mxnet,zhreshold/mxnet,szha/mxnet,apache/incubator-mxnet,mbaijal/incubator-mxnet,szha/mxnet,sxjscience/mxnet,larroy/mxnet,sxjscience/mxnet,tlby/mxnet,larroy/mxnet,larroy/mxnet,ForkedReposBak/mxnet,eric-haibin-lin/mxnet,dmlc/mxnet,larroy/mxnet,reminisce/mxnet,ptrendx/mxnet,reminisce/mxnet,dmlc/mxnet,szha/mxnet,zhreshold/mxnet,zhreshold/mxnet,DickJC123/mxnet,mbaijal/incubator-mxnet,yajiedesign/mxnet,ptrendx/mxnet,DickJC123/mxnet,zhreshold/mxnet,dmlc/mxnet,sxjscience/mxnet,tlby/mxnet,eric-haibin-lin/mxnet,tlby/mxnet,tlby/mxnet,reminisce/mxnet,szha/mxnet,DickJC123/mxnet,reminisce/mxnet,mbaijal/incubator-mxnet,tlby/mxnet,ForkedReposBak/mxnet,larroy/mxnet,dmlc/mxnet,ForkedReposBak/mxnet,leezu/mxnet,leezu/mxnet,sxjscience/mxnet,yajiedesign/mxnet,mbaijal/incubator-mxnet,ptrendx/mxnet,zhreshold/mxnet,yajiedesign/mxnet,dmlc/mxnet,leezu/mxnet,yajiedesign/mxnet,zhreshold/mxnet,sxjscience/mxnet,ForkedReposBak/mxnet,eric-haibin-lin/mxnet,dmlc/mxnet,mbaijal/incubator-mxnet,zhreshold/mxnet,ptrendx/mxnet,tlby/mxnet,eric-haibin-lin/mxnet,szha/mxnet,szha/mxnet,apache/incubator-mxnet,zhreshold/mxnet,ForkedReposBak/mxnet,ForkedReposBak/mxnet,yajiedesign/mxnet,tlby/mxnet,reminisce/mxnet,larroy/mxnet,zhreshold/mxnet,dmlc/mxnet,apache/incubator-mxnet,apache/incubator-mxnet,szha/mxnet,tlby/mxnet,eric-haibin-lin/mxnet,ptrendx/mxnet,yajiedesign/mxnet,sxjscience/mxnet,leezu/mxnet,larroy/mxnet,leezu/mxnet,reminisce/mxnet,mbaijal/incubator-mxnet,ForkedReposBak/mxnet,ForkedReposBak/mxnet,yajiedesign/mxnet