cmd/dist: fatal shouldn't print errstr on Plan 9

During change 1864 discussion, Russ Cox pointed out
the fatal function shouldn't print errstr.

Change-Id: Icd71ec04be9c944bc235b8b198158465172e4fde
Reviewed-on: https://go-review.googlesource.com/2030
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
test: disable bug248 and bug345 tests on Plan 9

These tests were enabled as part of change 1774.
They depend on the errchk tool, which is a Perl
script. However, Perl is not available on Plan 9.

Change-Id: I82707aae16013acc9a3800d39b0084588b852b53
Reviewed-on: https://go-review.googlesource.com/2031
Reviewed-by: Minux Ma <minux@golang.org>