[ux] Add a message to explain that the app is being removed if the install fails

locales/en.json

@@ -40,6 +40,7 @@
     "app_requirements_checking": "Checking required packages for {app}…",
     "app_requirements_failed": "Some requirements are not met for {app}: {error}",
     "app_requirements_unmeet": "Requirements are not met for {app}, the package {pkgname} ({version}) must be {spec}",
+    "app_remove_after_failed_install": "Removing the app following the installation failure…",
     "app_sources_fetch_failed": "Could not fetch sources files, is the URL correct?",
     "app_start_install": "Installing the app '{app}'…",
     "app_start_remove": "Removing the app '{app}'…",

src/yunohost/app.py

@@ -1026,6 +1026,8 @@ def app_install(operation_logger, app, label=None, args=None, no_remove_on_failu
             # This option is meant for packagers to debug their apps more easily
             if no_remove_on_failure:
                 raise YunohostError("The installation of %s failed, but was not cleaned up as requested by --no-remove-on-failure." % app_id, raw_msg=True)
+            else:
+                logger.warning(m18n.n("app_remove_after_failed_install"))
 
             # Setup environment for remove script
             env_dict_remove = {}