Fix test-program failures

Due to recent changes, mxs::MessageQueue::init() must be called
explicitly, if a monitor is created.

server/modules/monitor/mariadbmon/test/test_cycle_find.cc

@@ -19,6 +19,7 @@
 #include <sstream>
 #include <vector>
 #include <maxscale/alloc.h>
+#include <maxscale/messagequeue.hh>
 #include <set>
 
 using std::string;
@@ -69,6 +70,8 @@ private:
 
 int main()
 {
+    mxs::MessageQueue::init();
+
     MariaDBMonitor::Test tester;
     return tester.run_tests();
 }