Move zsh related varaibles to top level group vars

ansible/group_vars/all

 ---
+  zsh_ver: 5.7.1
+  zsh_src_url: "https://www.zsh.org/pub/old/zsh-{{ zsh_ver }}.tar.xz"
   yum_repo_files: []
   pkg_list: []

ansible/roles/cheaha.node/vars/main.yml

 ---
 # vars file for cheaha.node
-  zsh_ver: 5.7.1
-  zsh_src_url: "https://www.zsh.org/pub/old/zsh-{{ zsh_ver }}.tar.xz"