tests: fix various object leaks at tests framework level

The most important change is doing vm.close() when removing domain -
this means it wouldn't be cleaned later by iterating over app.domains.

Other changes include removing VMs in the right order, regarding netvm
dependency (otherwise killing or removing may fail). And one more
missing coroutine handling (in shutdown_and_wait).

qubes/tests/__init__.py

@@ -761,6 +761,7 @@ class SystemTestCase(QubesTestCase):
             pass
 
         del app.domains[vm.qid]
+        vm.close()
         del vm
 
         app.save()
@@ -828,10 +829,27 @@ class SystemTestCase(QubesTestCase):
             pass
 
     def remove_vms(self, vms):
+        vms = list(vms)
+        if not vms:
+            return
+        # break dependencies
         for vm in vms:
+            vm.default_dispvm = None
+        # then remove in reverse topological order (wrt netvm), using naive
+        # algorithm
+        # this heavily depends on lack of netvm loops
+        while vms:
+            vm = vms.pop(0)
+            # make sure that all connected VMs are going to be removed,
+            # otherwise this will loop forever
+            assert all(x in vms for x in vm.connected_vms)
+            if list(vm.connected_vms):
+                # if still something use this VM, put it at the end of queue
+                # and try next one
+                vms.append(vm)
+                continue
             self._remove_vm_qubes(vm)
 
-
     def remove_test_vms(self, xmlpath=XMLPATH, prefix=VMPREFIX):
         '''Aggresively remove any domain that has name in testing namespace.
         '''
@@ -843,8 +861,10 @@ class SystemTestCase(QubesTestCase):
                     app = self.app
                 except AttributeError:
                     app = qubes.Qubes(xmlpath)
-                self.remove_vms(vm for vm in app.domains
-                    if vm.name.startswith(prefix))
+                self.remove_vms([vm for vm in app.domains
+                    if vm.name.startswith(prefix)])
+                if not hasattr(self, 'app'):
+                    app.close()
                 del app
             except qubes.exc.QubesException:
                 pass
@@ -927,13 +947,15 @@ class SystemTestCase(QubesTestCase):
         subprocess.check_call(command)
 
     def shutdown_and_wait(self, vm, timeout=60):
-        vm.shutdown()
+        self.loop.run_until_complete(vm.shutdown())
         while timeout > 0:
             if not vm.is_running():
                 return
             self.loop.run_until_complete(asyncio.sleep(1))
             timeout -= 1
-        self.fail("Timeout while waiting for VM {} shutdown".format(vm.name))
+        name = vm.name
+        del vm
+        self.fail("Timeout while waiting for VM {} shutdown".format(name))
 
     def prepare_hvm_system_linux(self, vm, init_script, extra_files=None):
         if not os.path.exists('/usr/lib/grub/i386-pc'):