ssh exit with non-zero status on disabled user (#472)

It is confusing for scripts, where a disabled user has been specified,
that ssh exits with a zero status by default without indication anything
failed.

I think exitting with a non-zero status would make more clear in scripts
and automated setups where things failed, thus making noticing the issue
and debugging easier.

Signed-off-by: Eduardo Otubo <otubo@redhat.com>
Signed-off-by: Aleksandar Kostadinov <akostadi@redhat.com>

LP: #1170059

cloudinit/ssh_util.py

@@ -40,11 +40,13 @@
     "ssh-rsa-cert-v01@openssh.com",
 )
 
+_DISABLE_USER_SSH_EXIT = 142
 
 DISABLE_USER_OPTS = (
     "no-port-forwarding,no-agent-forwarding,"
     "no-X11-forwarding,command=\"echo \'Please login as the user \\\"$USER\\\""
-    " rather than the user \\\"$DISABLE_USER\\\".\';echo;sleep 10\"")
+    " rather than the user \\\"$DISABLE_USER\\\".\';echo;sleep 10;"
+    "exit " + str(_DISABLE_USER_SSH_EXIT) + "\"")
 
 
 class AuthKeyLine(object):

doc/examples/cloud-config.txt

@@ -236,7 +236,7 @@ disable_root: false
 # The string '$USER' will be replaced with the username of the default user.
 # The string '$DISABLE_USER' will be replaced with the username to disable.
 #
-# disable_root_opts: no-port-forwarding,no-agent-forwarding,no-X11-forwarding,command="echo 'Please login as the user \"$USER\" rather than the user \"$DISABLE_USER\".';echo;sleep 10"
+# disable_root_opts: no-port-forwarding,no-agent-forwarding,no-X11-forwarding,command="echo 'Please login as the user \"$USER\" rather than the user \"$DISABLE_USER\".';echo;sleep 10;exit 142"
 
 # disable ssh access for non-root-users
 # To disable ssh access for non-root users, ssh_redirect_user: true can be