Clarify common 500 errors

module_build_service/common/messaging.py

@@ -48,7 +48,9 @@ def publish(topic, msg, conf, service):
         return rv
     except Exception:
         messaging_tx_failed_counter.inc()
-        raise
+        raise RuntimeError(
+            "Unable to send message to backend %r" % conf.messaging
+        )
 
 
 def _fedmsg_publish(topic, msg, conf, service):

module_build_service/common/scm.py

@@ -226,7 +226,7 @@ class SCM(object):
                         "checkout: The requested commit hash was not found within the repository. "
                         "Perhaps you forgot to push. The original message was: %s" % str(e)
                     )
-                raise
+                raise RuntimeError("Unable to checkout module from SCM: %s" % e)
 
             timestamp = SCM._run(["git", "show", "-s", "--format=%ct"], chdir=self.sourcedir)[1]
             self.version = provide_module_stream_version_from_timestamp(timestamp=timestamp)