vmimage.subr: Redirect etcupdate log to stdout

[cperciva]

Summary

While we're here, send the etcupdate log from generating base.txz
to stdout instead of /dev/null (see e972e408d19a) as well.

MFC after: 1 week
Sponsored by: Amazon

[emaste]

Makes sense, but as @jrtc27 suggested on IRC what about -L /dev/stdout so that the -L output ends up in the build log?

[cperciva]

In D48719#1111350, @emaste wrote:

Makes sense, but as @jrtc27 suggested on IRC what about -L /dev/stdout so that the -L output ends up in the build log?

I'm fine with doing that if @gordon agrees to make the same change in release/Makefile. I figured the two places should be the same, one way or another.

[gordon]

As long as it doesn't end up as a build product, makes sense to me. Want to update the review with a new patch and we'll go from there?

[emaste]

In D48719#1111422, @cperciva wrote:

I'm fine with doing that if @gordon agrees to make the same change in release/Makefile. I figured the two places should be the same, one way or another.

Yep, agree they should be the same. I'm fine with doing this with whatever sequence of commits folks like. Both could be switched after this commit goes in.

[jrtc27]

Probably best to land this, since it's actually important for reproducibility, then we can update both to something else later that gives extra visibility into the build less urgently

[cperciva]

Use stdout instead

[cperciva]

I figure it's easier to do this in one commit rather than making a change and then changing it again. Looks ok to everyone?