Disable execution of tests for plasma-integration.

This is necessary to ensure CI nodes do not become blocked due to hanging tests withing plasma-integration.

Currently, plasma-integration has several tests that make use of KIO slaves directly (skipping KLauncher).
Unfortunately, they do not terminate the slaves prior to the conclusion of the test, resulting in the kioslave processes being left around afterwards.
This is a condition that CTest will not tolerate, leading to it waiting indefinitely for these processes to exit - and in turn blocking all other builds on the CI node in question.
While this is not a major issue in the case of Linux builds, it can quickly become a severe condition in the case of FreeBSD and Windows builds due to those builders being fixed rather than dynamically allocated.

This class of issue (CTest waiting due to resident processes being left behind) has been a major issue as of late and is quickly leading to the CI system becoming unmaintainable due to the level of breakage.
Should it be necessary to ensure the maintainability of the system, withdrawal of execution of tests for all projects is an option currently under consideration.

CCMAIL: plasma-devel@kde.org
CCMAIL: kde-frameworks-devel@kde.org
CCMAIL: release-team@kde.org
CCMAIL: kdevelop-devel@kde.org
CCMAIL: sysadmin@kde.org