s3:rpclient: rpclient help is not very helpful

s3:rpclient: rpclient help is not very helpful

The help was not telling me that there was a mandatory 'server' argument
that I needed to specify. After trying several different combinations
of parameters, I eventually had to run the tool in gdb to work out why
it was complaining.

This is the output I was getting:

bin/rpcclient -U$USERNAME%$PASSWORD -I $SERVER_IP
Usage: rpcclient [OPTION...]
  -c, --command=COMMANDS                 Execute semicolon separated
cmds
  -I, --dest-ip=IP                       Specify destination IP address
  -p, --port=PORT                        Specify port number
...

New help output is:

Usage: rpcclient [OPTION...] <server>
Options:
  -c, --command=COMMANDS                 Execute semicolon separated
cmds
...

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Ralph Boehme <slow@samba.org>