[autotests] Wrap integration tests in dbus-session-run

Each test needs a dedicated dbus session as the test needs to register
services (e.g. kglobalaccel) and might fail if that cannot be registered.

Due to the wrapping in another command the test need to make sure that
any process they start terminates before them. E.g. the activities test
must stop kactivitymanagerd in cleanupTestCase, otherwise the test times
out.