rpc: socket: Explicitly error if we exceed retry count

rpc: socket: Explicitly error if we exceed retry count

When we autolaunch libvirtd for session URIs, we spin in a retry
loop waiting for the daemon to start and the connect(2) to succeed.

However if we exceed the retry count, we don't explicitly raise an
error, which can yield a slew of different error messages elsewhere
in the code.

Explicitly raise the last connect(2) failure if we run out of retries.