 [MXNET-696][PYTHON][UNDEFINED NAME] import logging in ci/util.py (#12488)
 [MXNET-696][PYTHON][UNDEFINED NAME] import logging in ci/util.py (#12488)

Fixes #12406 @larroy @marcoabreu @szha 

[flake8](http://flake8.pycqa.org) testing of https://github.com/apache/incubator-mxnet on Python 3.7.0

$ __flake8 . --count --select=E901,E999,F821,F822,F823 --show-source --statistics__
```
./ci/util.py:73:21: F821 undefined name 'logging'
                    logging.warning("Exception: %s, Retrying in %d seconds...", str(e), mdelay)
                    ^
1     F821 undefined name 'logging'
1
```
reminisce/mxnet,leezu/mxnet,eric-haibin-lin/mxnet,zhreshold/mxnet,szha/mxnet,szha/mxnet,DickJC123/mxnet,leezu/mxnet,ForkedReposBak/mxnet,reminisce/mxnet,reminisce/mxnet,tlby/mxnet,eric-haibin-lin/mxnet,dmlc/mxnet,larroy/mxnet,mbaijal/incubator-mxnet,ptrendx/mxnet,zhreshold/mxnet,tlby/mxnet,larroy/mxnet,larroy/mxnet,yajiedesign/mxnet,reminisce/mxnet,szha/mxnet,DickJC123/mxnet,yajiedesign/mxnet,mbaijal/incubator-mxnet,szha/mxnet,ptrendx/mxnet,dmlc/mxnet,yajiedesign/mxnet,ptrendx/mxnet,ForkedReposBak/mxnet,zhreshold/mxnet,szha/mxnet,ptrendx/mxnet,tlby/mxnet,szha/mxnet,mbaijal/incubator-mxnet,mbaijal/incubator-mxnet,larroy/mxnet,szha/mxnet,ptrendx/mxnet,dmlc/mxnet,dmlc/mxnet,tlby/mxnet,DickJC123/mxnet,larroy/mxnet,eric-haibin-lin/mxnet,dmlc/mxnet,reminisce/mxnet,ptrendx/mxnet,yajiedesign/mxnet,leezu/mxnet,leezu/mxnet,DickJC123/mxnet,eric-haibin-lin/mxnet,apache/incubator-mxnet,zhreshold/mxnet,yajiedesign/mxnet,eric-haibin-lin/mxnet,sxjscience/mxnet,ptrendx/mxnet,dmlc/mxnet,leezu/mxnet,sxjscience/mxnet,tlby/mxnet,sxjscience/mxnet,reminisce/mxnet,yajiedesign/mxnet,sxjscience/mxnet,apache/incubator-mxnet,zhreshold/mxnet,dmlc/mxnet,mbaijal/incubator-mxnet,yajiedesign/mxnet,reminisce/mxnet,ForkedReposBak/mxnet,ForkedReposBak/mxnet,reminisce/mxnet,leezu/mxnet,leezu/mxnet,tlby/mxnet,leezu/mxnet,ForkedReposBak/mxnet,tlby/mxnet,reminisce/mxnet,larroy/mxnet,leezu/mxnet,ptrendx/mxnet,zhreshold/mxnet,ForkedReposBak/mxnet,zhreshold/mxnet,tlby/mxnet,zhreshold/mxnet,ForkedReposBak/mxnet,larroy/mxnet,sxjscience/mxnet,eric-haibin-lin/mxnet,zhreshold/mxnet,larroy/mxnet,sxjscience/mxnet,dmlc/mxnet,ptrendx/mxnet,eric-haibin-lin/mxnet,eric-haibin-lin/mxnet,mbaijal/incubator-mxnet,sxjscience/mxnet,tlby/mxnet,szha/mxnet,yajiedesign/mxnet,tlby/mxnet,larroy/mxnet,ForkedReposBak/mxnet,apache/incubator-mxnet,ptrendx/mxnet,eric-haibin-lin/mxnet,szha/mxnet,mbaijal/incubator-mxnet,dmlc/mxnet,ForkedReposBak/mxnet,sxjscience/mxnet,yajiedesign/mxnet,mbaijal/incubator-mxnet,apache/incubator-mxnet,reminisce/mxnet,sxjscience/mxnet,mbaijal/incubator-mxnet