Clear integration configs cache before each test case

Review Request #8915 — Created April 26, 2017 and submitted — Latest diff uploaded

Information

rbintegrations
master
757986c...

Reviewers

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.