x/crypto/ssh: bail early if a server has no auth methods configured.

Change-Id: I58fdfbe00fcc4ca09da9699edcc181cc512feef7
Reviewed-on: https://go-review.googlesource.com/9807
Reviewed-by: JP Sugarbroad <jpsugar@google.com>
Reviewed-by: Adam Langley <agl@golang.org>
2 files changed