Read the ExtORPort cookie on every call to DialOr.
Read the ExtORPort cookie on every call to DialOr.

This works around tor bug #15240, where the ExtORPort cookie is
generated after the pluggable transports are launched, leading to a
race condition and DialOr failures.

'ServerInfo.AuthCookie' is deprecated by this change, replaced by
'ServerInfo.AuthCookiePath', however nothing external to goptlib should
be using either value in most situations.

Yawning/goptlib,wyuelin/mygoptlib