As proposed by @laanwj the error message is now prefixed with the
"timeout on transient error:" prefix, to explain why the error is
suddenly considered terminal.
Adds a new numeric `-rpcwaittimeout` that can be used to limit the
time we spend waiting on the RPC server to appear. This is used by
downstream projects to provide a bit of slack when `bitcoind`s RPC
interface is not available right away.
Christian Decker