Use up to 10 request attempts with 0.05 second pause in between.

This is used in GET polling step only at the moment.
GET polling: do not cover final assertion line
GET polling: adjust scenario description
Add BasicAuth test
Misc PEP8 cleanups
setup.py: do not inject test deps
testserver: move poll counter to the top
Add requirements_dev.txt for development and travis
Initial travis configuration