RHEL: Move zlib-devel to cinder_devel_distro_packages

This last devel package was missed in both of these
reviews:
- https://review.openstack.org/614334
- https://review.openstack.org/615443

Change-Id: Ia0c935929bf771aa720d7da7ff2875fde9159156

vars/redhat-7.yml

@@ -24,7 +24,6 @@ cinder_distro_packages:
   - nfs-utils
   - rpcbind
   - which
-  - zlib-devel
 
 cinder_service_distro_packages:
   - openstack-cinder
@@ -40,6 +39,7 @@ cinder_devel_distro_packages:
   - kmod-devel
   - postgresql-devel
   - systemd-devel
+  - zlib-devel
 
 cinder_volume_distro_packages:
   - qemu-img-ev