tests/monitor-unit-tests: Run a client while testing

Run a client while testing and check that it's alive when checking each
monitor configuration.

https://bugzilla.gnome.org/show_bug.cgi?id=730551

src/tests/monitor-unit-tests.h

@@ -22,4 +22,8 @@
 
 void init_monitor_tests (void);
 
+void pre_run_monitor_tests (void);
+
+void finish_monitor_tests (void);
+
 #endif /* MONITOR_UNIT_TESTS_H */