Make aodh tempest tests work with Python3

With Python3 aodh tests fails with below Error,
this patch fixes it:-

TypeError: a bytes-like object is required, not 'str'

Change-Id: I447c384a280e6225f3617a251314b307855d6025
Closes-Bug: #1809802
diff --git a/telemetry_tempest_plugin/aodh/service/client.py b/telemetry_tempest_plugin/aodh/service/client.py
index 1043a05..a2361a8 100644
--- a/telemetry_tempest_plugin/aodh/service/client.py
+++ b/telemetry_tempest_plugin/aodh/service/client.py
@@ -29,7 +29,7 @@
     uri_prefix = "v2"
 
     def deserialize(self, body):
-        return json.loads(body.replace("\n", ""))
+        return json.loads(body.decode('utf-8').replace("\n", ""))
 
     def serialize(self, body):
         return json.dumps(body)