Report client.get_profile() errors nicely (e.g. API key).

This patch is particularly useful in the scenario that your
API key is wrong or out of date, but it's targeted more
generally at any error that `client.get_profile()` reports.

zulip_bots/zulip_bots/lib.py

@@ -106,6 +106,13 @@ class ExternalBotHandler(object):
                 '''.format(e))
             sys.exit(1)
 
+        if user_profile.get('result') == 'error':
+            msg = user_profile.get('msg', 'unknown')
+            print('''
+                ERROR: {}
+                '''.format(msg))
+            sys.exit(1)
+
         self._rate_limit = RateLimit(20, 5)
         self._client = client
         self._root_dir = root_dir