Add reno to tempest

Tempest is going to be on pypi and expose a stable interface in
the tempest.lib namespace, so adding reno to it.

Partially-implements: bp tempest-lib-reintegration
Change-Id: Ice4c27f7bc6d0154cfced9789f3c82236106a9e3
diff --git a/.gitignore b/.gitignore
index d58b162..5b87cec 100644
--- a/.gitignore
+++ b/.gitignore
@@ -23,3 +23,6 @@
 !.coveragerc
 cover/
 doc/source/_static/tempest.conf.sample
+
+# Files created by releasenotes build
+releasenotes/build