Clear integration configs cache before each test case
Review Request #8915 — Created April 26, 2017 and submitted
The integration configs cache needs to be cleared, otherwise a configuration
from one test case will remain and possibly interfere with subsequent tests.
The change uncovered one problematic Slack test case, which has been fixed.
Also, the .gitignore had a typo: .nodeids instead of .noseids.
All unit tests pass.