[autotests] Stabilise colorcorrect test

Summary:
It crashes occasionally as the connection thread is still processing events
when the app is tearing down. These changes bring it in line with the
other tests using WAYLANDTEST_MAIN.

Test Plan:
Relevant test now passes.
Ran repeatedl without a crash

Reviewers: #kwin

Subscribers: kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D17254