afscp: Always show fetch/store errors

When we get an error from a fetch or store operation, show what the
error was, instead of just saying "some network error occured".

Reviewed-on: http://gerrit.openafs.org/3290
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 8078c4dcf2dd5a922225f0e37babf1b357b5e72d)

Change-Id: Icfdce08149e16749097bd6be326312dec6292d34
Reviewed-on: http://gerrit.openafs.org/9415
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>