Don't run prospector over test packages

I don't believe we should be penalised on "application health" for
adding a bunch of clear unit test functions without docstrings.

Also, there are some py.test patterns (such as function parameters
shadowing global fixture functions) which cause pylint to whine but
which are absolutely fine in context.

.prospector.yaml

@@ -1,6 +1,5 @@
output-format: grouped
strictness: veryhigh
test-warnings: true
doc-warnings: true
max-line-length: 79
pep8: