cmd/dist: convert host tests to use goTest
cmd/dist: convert host tests to use goTest

This adds support for host tests to goTest and registerTest and
modifies all uses of registerHostTest to use goTest and registerTest.

This eliminates the last case where go test command lines are
constructed by hand. Next we'll clean up all of the infrastructure
support for that.

I traced all exec calls from cmd/dist on linux/amd64 and this makes
only no-op changes (such as re-arranging the order of flags).

Preparation for #37486.

Change-Id: Icb7ec8efdac72bdb819ae24b2f585375d9d9d5b9
Reviewed-on: https://go-review.googlesource.com/c/go/+/450019
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
Run-TryBot: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go