client: combine client_open() and client_parse_config()

client: combine client_open() and client_parse_config()

Both users (client.c and audiod.c) called client_open() right
after calling client_parse_config(), so call client_open() from
client_parse_config() and make client_open() static.

While we're at it, rename client_open() to client_connect() as this
is what the function does. Also rename client_parse_config() to
client_open() and change audiod.c and client.c to call client_open()
instead of client_parse_config().

This patch fixes a segfault in para_client was it was run without
specifying a command. In this case, the private client data struct
was used by para_log after being freed -- Ouch. Fortunately, this
bug didn't affect para_audiod as it never calls these functions with
no command.

Another bug due to a typo in client_close() is also fixed. This code
needs closer investigation and lacks documentation btw.