wcst_import enable GDAL exception when opening file

[Bang Pham Huu]

By default the GDAL/OGR Python bindings do not raise exceptions when errors occur. Instead they return an error value such as None and write an error message to sys.stdout. You can enable exceptions by calling the UseExceptions() function:

from osgeo import gdal

# Enable GDAL/OGR exceptions
gdal.UseExceptions()

In case wcst_import opens 1 file with GDAL and it fails (due to file is not available), depending on if skip:true, it will ignore the file or throws an exception.