Don't require specific version of openstack-pkg-tools

So build will work on older debian/ubuntu releases
diff --git a/debian/control b/debian/control
index e5d5a54..1def884 100644
--- a/debian/control
+++ b/debian/control
@@ -3,7 +3,7 @@
 Section: admin
 Priority: optional
 Build-Depends: debhelper (>= 9),
-               openstack-pkg-tools (>= 43~),
+               openstack-pkg-tools,
                salt-master,
                python,
                python-yaml,