fix: [0km] make ``vps-install`` catch key in more scenario and error message more clear

The new way doesn't overwrite ``$out`` which helps displaying a
meaningful message. The change allows also stdout and stderr mixing,
that would not guarantee that the key appears as the last command.

bin/0km

@@ -768,10 +768,17 @@ vps_install_backup() {
         return 1
     fi
 
-    out="${out%$'\n'}"
-    out="${out#*$'\n'}"
-    key="${out%\'*}"
-    key="${key##*\'}"
+    ## Format of output:
+    ##
+    ## II Entry for service rsync-backup is already present in '/opt/apps/myc-deploy/compose.yml'.
+    ## II You can run this following command from an host having admin access to core-07.0k.io:
+    ##    (Or send it to a backup admin of core-07.0k.io)
+    ## ssh -p 10023 myadmin@core-07.0k.io ssh-key add 'ssh-rsa AAAAAAAD...QCJ\
+    ## 8HH6pVgEpu1twyxpr9xTt7eh..WaJdgPoxmiEwGfjMMNGxs39ggOTKUuSFSmOv8TiA1fzY\
+    ## s85hF...dKP1qByJU1k= compose@odoo.sikle.fr'
+
+    key="ssh-rsa ${out##*\'ssh-rsa }"  ## remove everything before last "'ssh-rsa"
+    key="${key%\'*}"                   ## remove everything after last '
 
     if ! [[ "$key" =~ ^"ssh-rsa "[a-zA-Z0-9/+=]+" "[a-zA-Z0-9._-]+"@"[a-zA-Z0-9._-]+$ ]]; then
         err "Unexpected output from 'vps install backup $server'. Can't find key."