moutnroot failing on zpools in Azure after upgrade from 10 to 11 due to lack of waiting for da0

[Pete French]

> The variable still exists but is ignored when using ZFS.
>
> It's a known issue. You could try this patch:
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D208882#c3

Ah, OK, thanks...

> Manually specifying the root pool should workaround the issue.

Interesting, I didnt think of trying that. Mainly because it appears to
have set the variable correctly, or at least it has the output:

	Trying to mount root from zfs:rpool/ROOT/default 

But I shall try that. As soon as I can get one of them up
and running again :-( I now have zero machines booting! My
diagnosis that it was due to the size of the Vm was wrong, and I rebooted
them on the smallest size thinking it would be fine. It wasn't.

*sigh*

Thankyou!