test_providing_resource_to_stub_treq runs too long

[dmurvihill]

StubbingTests.test_providing_resource_to_stub_treq tests 1,080 combinations of verb, URL, params, headers, and data. This takes almost 20 seconds on my machine each time this one unit test is run. Given the number of different environments Treq supports this is very annoying.

A test that checks a limited subset of this space -- say, 20 combinations -- would run almost instantly and provide almost the same level of confidence as the more thorough test. I would be happy to implement this change.