pbr.version.VersionInfo needs package name (oslo.xyz and not oslo_xyz)

We need to pass into VersionInfo what one would expect from running:
 setup.py --name

 Right now we pass in say oslo_context and pbr fails if there is no .git in
  the python source tree

  Closes-Bug: #1662266

Change-Id: I45d2edddfd516f65e1589e9b7816f1256e3f0d24

oslo_messaging/version.py

@@ -15,4 +15,4 @@
 
 import pbr.version
 
-version_info = pbr.version.VersionInfo('oslo_messaging')
+version_info = pbr.version.VersionInfo('oslo.messaging')