[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