e2e: Switch from coroutines to async, for python3.8

tests/end_to_end/__main__.py

@@ -108,9 +108,9 @@ class XMPPComponent(slixmpp.BaseXMPP):
             if self.biboumi:
                 self.biboumi.stop()
 
-    @asyncio.coroutine
+
-    def accept_routine(self):
+    async def accept_routine(self):
-        self.accepting_server = yield from self.loop.create_server(lambda: self,
+        self.accepting_server = await self.loop.create_server(lambda: self,
                                                               "127.0.0.1", 8811, reuse_address=True)
 
     def check_stanza_against_all_expected_xpaths(self):
@@ -220,13 +220,11 @@ class ProcessRunner:
         self.signal_sent = False
         self.create = None
 
-    @asyncio.coroutine
+    async def start(self):
-    def start(self):
+        self.process = await self.create
-        self.process = yield from self.create
 
-    @asyncio.coroutine
+    async def wait(self):
-    def wait(self):
+        code = await self.process.wait()
-        code = yield from self.process.wait()
         return code
 
     def stop(self):