cildataconverter.py needs to gracefully handle invalid zip files

[coleslaw481]

Example of failure:

2017-10-09 14:23:37,515 DEBUG cildata_util.cildataconverter 25696.tif
2017-10-09 14:23:37,630 ERROR cildata_util.dbutil 25696.tif did not have a successful download. Skipping...
2017-10-09 14:23:37,630 DEBUG cildata_util.cildataconverter Making backup of /home/churas/tasks/cil_downloader/converted_images/images/25696/25696.json
2017-10-09 14:23:37,690 DEBUG cildata_util.cildataconverter Entry file name: 25696.tif and cdf file name: 25696.tif
2017-10-09 14:23:37,690 INFO cildata_util.cildataconverter Updating 25696.tif
2017-10-09 14:23:37,690 DEBUG cildata_util.cildataconverter Appending to list
2017-10-09 14:23:37,690 DEBUG cildata_util.cildataconverter Entry file name: 25696.jpg and cdf file name: 25696.tif
2017-10-09 14:23:37,691 DEBUG cildata_util.cildataconverter Entry file name: 25696.raw and cdf file name: 25696.tif
2017-10-09 14:23:37,693 DEBUG cildata_util.dbutil Writing out json file to /home/churas/tasks/cil_downloader/converted_images/images/25696/25696.json
2017-10-09 14:23:37,693 DEBUG cildata_util.cildataconverter 25696.jpg
2017-10-09 14:23:37,693 DEBUG cildata_util.cildataconverter Making backup of /home/churas/tasks/cil_downloader/converted_images/images/25696/25696.json
2017-10-09 14:23:37,696 DEBUG cildata_util.cildataconverter Entry file name: 25696.tif and cdf file name: 25696.jpg
2017-10-09 14:23:37,696 DEBUG cildata_util.cildataconverter Entry file name: 25696.jpg and cdf file name: 25696.jpg
2017-10-09 14:23:37,696 INFO cildata_util.cildataconverter Updating 25696.jpg
2017-10-09 14:23:37,696 DEBUG cildata_util.cildataconverter Appending to list
2017-10-09 14:23:37,696 DEBUG cildata_util.cildataconverter Entry file name: 25696.raw and cdf file name: 25696.jpg
2017-10-09 14:23:37,699 DEBUG cildata_util.dbutil Writing out json file to /home/churas/tasks/cil_downloader/converted_images/images/25696/25696.json
2017-10-09 14:23:37,724 DEBUG cildata_util.cildataconverter 25696.raw
2017-10-09 14:23:37,847 DEBUG cildata_util.dbutil Making copy of /home/churas/tasks/cil_downloader/converted_images/images/25696/25696.raw naming it /home/churas/tasks/cil_downloader/converted_images/images/25696/25696.zip
2017-10-09 14:26:34,972 ERROR cildata_util.cildataconverter Caught fatal exception
Traceback (most recent call last):
File "/usr/bin/cildataconverter.py", line 154, in main
return _convert_data(theargs)
File "/usr/bin/cildataconverter.py", line 107, in _convert_data
newcdfs = converter.convert(cdf, base_dir)
File "/usr/lib/python2.7/site-packages/cildata_util/dbutil.py", line 839, in convert
return self._convert_image(cdf, cdf_dir)
File "/usr/lib/python2.7/site-packages/cildata_util/dbutil.py", line 878, in _convert_image
extracted_cdfs = self._extract_image_from_zip(cdf, cdf_dir)
File "/usr/lib/python2.7/site-packages/cildata_util/dbutil.py", line 906, in _extract_image_from_zip
extracted_file = zf.extract(zentry, path=tmpdir)
File "/usr/lib64/python2.7/zipfile.py", line 1024, in extract
return self._extract_member(member, path, pwd)
File "/usr/lib64/python2.7/zipfile.py", line 1078, in _extract_member
with self.open(member, pwd=pwd) as source,
File "/usr/lib64/python2.7/zipfile.py", line 967, in open
raise BadZipfile("Bad magic number for file header")
BadZipfile: Bad magic number for file header