all: update to new errors interface
all: update to new errors interface

Change-Id: I7080de13b2f44ad6b8eabce4e4598c2f5a6400d1
Reviewed-on: https://upspin-review.googlesource.com/16780
Reviewed-by: Andrew Gerrand <395a7d33bec8475c9b83b7d440f141bcbd994aa5@golang.org>

upspin/aws