[release-branch.go1.14] cmd/go: fix parallel chatty tests on solaris-amd64 builder

The parallel chatty tests added in CL 229085 fail on the
solaris-amd64-oraclerel builder, because a +NN:NN offset time zone is
used. Allow for the `+` character in the corresponding regex to fix
these tests. Also move the '-' to the end of the character class, so it
is not interpreted as the range 9-T.

Updates #38458.
For #39308.

Change-Id: Iec9ae82ba45d2490176f274f0dc6812666eae718
Reviewed-on: https://go-review.googlesource.com/c/go/+/234978


Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-on: https://go-review.googlesource.com/c/go/+/242059
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>