avoid ogr import failure when running tests

[cehbrecht]

Overview

This is a quick-fix to avoid import ogr exception when running tests without gdal.

Related Issue / Discussion

GDAL issue: #398

Additional Information

Contribution Agreement

(as per https://github.com/geopython/pywps/blob/master/CONTRIBUTING.rst#contributions-and-licensing)

• [ ] I'd like to contribute [feature X|bugfix Y|docs|something else] to PyWPS. I confirm that my contributions to PyWPS will be compatible with the PyWPS license guidelines at the time of contribution.
• [ x] I have already previously agreed to the PyWPS Contributions and Licensing Guidelines

[coveralls]

Coverage remained the same at 0.0% when pulling 5e035e75a6e5017959616fb208307fc7bc037783 on cehbrecht:fix-ogr-import into 633608274fa7b0fb48b6dd4208a2881d39ff5735 on geopython:pywps-4.4.

[cehbrecht]

ping @Zeitsperre