Instead of printing Atoi as function name for test failures
print the actual function name and arguments tested.

Add a base field to the parseUint64BaseTests for consistency with
the parseInt64BaseTests tests.

Change-Id: Ib9891bdb87b62672b4216625212acfe6474c70fc
Reviewed-on: https://go-review.googlesource.com/55136
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>