Update repo_build role for PBR fix

A new version of PBR was released which causes some services, like
gnocchi, to break in new and exciting ways. This change installs PBR
within the repo_build role which will ensure all of the correct tools
are available to the repo build process and are installed using known
constraints.

Change-Id: Ic21bf2ef50836f793d3c3549f2400ac05c6f751a

ansible-role-requirements.yml

@@ -133,7 +133,7 @@
 - name: repo_build
   scm: git
   src: https://git.openstack.org/openstack/openstack-ansible-repo_build
-  version: f5f9e1c390c0d1bc4b1ec2b8a1487aaa3a1095ab
+  version: eb46bd33b10c11cd3723e307faa8e5f82dae0ec1
 - name: repo_server
   scm: git
   src: https://git.openstack.org/openstack/openstack-ansible-repo_server