Fix: ui_context: crm cluster delete autocompletion #1403 #1460

If you type
  $ crm configure delete
of do it interactively
  $ crm configure
  crm(live/node1)configure# delete
and then double press tab it, should propose possible resource options.
And this commit makes it working again.

crmsh/ui_context.py

@@ -255,6 +255,9 @@ def enter_level(self, level):
         self._in_transit = True
 
         entry = level()
+        if level.name in ['configure']:
+            if 'requires' in dir(entry) and not entry.requires():
+                self.fatal_error("Missing requirements")
         self.stack.append(entry)
         self.clear_readline_cache()