It doesn't affect anything yet, but it's going to be used in the future for
network-specific behavior. It also renames short '--timeout' form to '-s'
avoiding conlict with '-t' used for '--testnet'.
This makes rpc flags consistent across all commands, previously some commands
used 'endpoint, e' and some 'rpc, r', some had ability to change timeout and
some hadn't. Now 'rpc-endpoint, r' is used everywhere along with 'timeout, t'.
