ubuntu:19.04 is not supported anymore and update repos are unavailable, so
build process on Linux just fails. Latest stable ubuntu:20.04 works fine.
Also, DEBIAN_FRONTEND=noninteractive env variable has been added to prevent
unneeded questions during installation of tzdata package.
Fixesgolang/go#38724
Change-Id: I2d7730d83fc051de2879d4f97fc7942090d2574c
Reviewed-on: https://go-review.googlesource.com/c/sys/+/230577
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>