Change used chars for kubeadm tokens (#1701)

inventory/group_vars/all.yml

@@ -87,8 +87,8 @@ bin_dir: /usr/local/bin
 
 ## Uncomment to enable experimental kubeadm deployment mode
 #kubeadm_enabled: false
-#kubeadm_token_first: "{{ lookup('password', 'credentials/kubeadm_token_first length=6  chars=ascii_letters,digits') }}"
-#kubeadm_token_second: "{{ lookup('password', 'credentials/kubeadm_token_second length=16 chars=ascii_letters,digits') }}"
+#kubeadm_token_first: "{{ lookup('password', 'credentials/kubeadm_token_first length=6  chars=ascii_lowercase,digits') }}"
+#kubeadm_token_second: "{{ lookup('password', 'credentials/kubeadm_token_second length=16 chars=ascii_lowercase,digits') }}"
 #kubeadm_token: "{{ kubeadm_token_first }}.{{ kubeadm_token_second }}"
 #
 ## Set these proxy values in order to update docker daemon to use proxies