model: refactor and simplify _get_instance _get_instance is a BaseModel method, but never uses "self". Instead it takes a class argument, which indicates that it's better suited as a classmethod on said classes. Also rename to something more descriptive, remove leading underscore since it's not a private API, and refactor for readability.

pytest>=2.7.0,<3.0
pytest-runner
pytest-sugar>=0.7.0,<1.0.0
pytest-catchlog
webtest==1.4.3
mock
sphinx