Add username argument to vcloud-login

vcloudtools/command/login.py

@@ -10,24 +10,25 @@
 log = logging.getLogger(__name__)
 parser = ArghParser()
 
-def login_if_needed(vcloud):
+def login_if_needed(vcloud, user):
     if vcloud.logged_in:
         log.info("Already logged in")
         return
 
     print("Please log into vCloud", file=sys.stderr)
-    username = _raw_input("Username: ")
+    username = user or _raw_input("Username: ")
     password = getpass("Password: ")
 
     vcloud.login(username, password)
 
+@arg('-u', '--user', help='Username', default=None)
 def login(args):
     """
     Log into a vCloud instance, and print the resulting auth token.
     """
     c = VCloudAPIClient()
 
-    login_if_needed(c)
+    login_if_needed(c, args.user)
 
     print("export {0}='{1}'".format(envkey('auth_token'), c.token))