Drop Python 3.4 and switch to async / await syntax for asyncio. Fixes #1425

tests/compute/virtualbox/test_virtualbox_manager.py

@@ -79,8 +79,7 @@ def test_list_vms(manager, loop):
                '"<inaccessible>" {42b4d095-ff5f-4ac4-bb9d-5f2c7861c1f1}',
                '"Linux Microcore 4.7.1" {ccd8c50b-c172-457d-99fa-dd69371ede0e}']
 
-    @asyncio.coroutine
-    def execute_mock(cmd, args):
+    async def execute_mock(cmd, args):
         if cmd == "list":
             return vm_list
         else: