Add server_id in exception ServerUnreachable

This is to add server_id in exception ServerUnreachable for the
convenience of debugging.

Change-Id: Ib31fe70fae33d5e2eb7cda6e02b03649918a546b
diff --git a/tempest/scenario/manager.py b/tempest/scenario/manager.py
index f889c44..b151375 100644
--- a/tempest/scenario/manager.py
+++ b/tempest/scenario/manager.py
@@ -664,7 +664,7 @@
             for address in addresses:
                 if address['version'] == CONF.validation.ip_version_for_ssh:
                     return address['addr']
-            raise exceptions.ServerUnreachable()
+            raise exceptions.ServerUnreachable(server_id=server['id'])
         else:
             raise exceptions.InvalidConfiguration()