para_client: Fix a memory leak.

The main function of para_client first calls client_parse_config()
to decide whether to start an interactive session, run in completion
mode or execute the given command. In the third case case we call
client_open() which calls client_parse_config() again, thereby
leaking the client_task structure which was returned by the first
call to client_parse_config().

Fix this leak by calling client_connect() instead of client_open().