S3A init hangs if you try to connect while the system is offline

F3A init hangs if you try to connect while the system is offline (that is: the nost of the s3 endpoint is unknown)

Assumption: unknown host exception is considered recoverable & client is spinning for a long time waiting for it.

I think we can conclude that unknown host is unrecoverable: if DNS is in trouble, you are doomed.

Proposed: quick lookup of endpoint addr, fail with our wiki diagnostics error on any problem.
I don't see any cost in doing this, as it will guarantee that the endpoint is cached in the JVM ready for the AWS client connection. If it can't be found, we'll fail within 20+s with something meaningful.

Noticed during a test run: laptop wifi off; all NICs other than loopback are inactive.