Disable starting kactivitymanagerd throughout launchertasksmodeltest

Summary:
Currently kactivitymanagerd is loaded halfway through this test, which
has the net result of just breaking.

The test doesn't need it and still passes without it.

Test Plan:
Ran the unit test that's been failing on CI for ages.
It used to fail locally (if run in a new session, see my email on
plasma-devel)
now it passes.

Reviewers: #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D3229

libtaskmanager/autotests/launchertasksmodeltest.cpp

@@ -46,6 +46,7 @@ class LauncherTasksModelTest : public QObject
 
 void LauncherTasksModelTest::initTestCase()
 {
+    qApp->setProperty("org.kde.KActivities.core.disableAutostart", true);
     m_urlStrings << QLatin1String("file:///usr/share/applications/org.kde.dolphin.desktop");
     m_urlStrings << QLatin1String("file:///usr/share/applications/org.kde.konsole.desktop");
 }