[mboximport] replace --url option by a required endpoint argument

mboximportclient.py

@@ -131,14 +131,14 @@ def main():
     parser = argparse.ArgumentParser(
             description='import email into a cubicweb instance')
     parser.add_argument(
-            '--url', metavar='url', type=str, required=True,
-            help='base url or name of the cubicweb instance')
+            'endpoint', metavar='endpoint', type=str,
+            help='cwclientlib endpoint of the cubicweb instance')
     parser.add_argument(
             'mbox', metavar='mailbox', type=argparse.FileType('r'),
             nargs='+', help='mbox files to import (- for stdin)')
     args = parser.parse_args()
 
-    proxy = cwproxy_for(args.url)
+    proxy = cwproxy_for(args.endpoint)
 
     importer = Importer(proxy)
     for f in args.mbox: