Issue 502 fix async

[cehbrecht]

Overview

This is an update of PR #451. If fixes the async keyword and the usage of the new FileStorageBuilder.

Related Issue / Discussion

Fix #502

Additional Information

Contribution Agreement

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

• [ x] 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

[cehbrecht]

@davidcaron @tomkralidis ok to merge to master?

Not sure if everything is fixed but it worked with the Emu WPS.

[coveralls]

Coverage remained the same at 75.132% when pulling f91bed60419ae2f7759037eb55c949500896938d on cehbrecht:issue-502-fix-async into f2704c8be835cabc25368ada65147fa1beb79cc0 on geopython:master.

[cehbrecht]

@tomkralidis thanks for quick response :)