Move Sleep process definition

[huard]

Overview

Moves the Sleep process class definition with other test processes to facilitate reuse.

Related Issue / Discussion

In response to comments in #657

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

[coveralls]

Coverage increased (+0.03%) to 81.087% when pulling 53ba8ac8910cba430d874066fc7986e7cae6a125 on huard:refactor_sleep_test into 85ca8191f1440e5906210408d2fa48c41f0ca679 on geopython:main.

[cehbrecht]

@huard looks good. Thanks :)