configure hook output not accessible

[Didier Roche-Tolomelli]

The output from configure hooks isn't accessible in /var/log/syslog or any other place I can think of. This is annoying especially when the hook fails for some reasons.

For instance, in /var/log/syslog, you can see:
Nov 8 10:15:14 localhost /usr/lib/snapd/snapd[1061]: taskrunner.go:353: DEBUG: Running task 82 on Do: Run configure hook of "basic-hooks" snap if present

But if the configure hook echo something are do anything invalid (like writing to SNAP_USER_DATA, which makes no sense under that paradigm as configure hooks are user-context-less), you don't get any debug info.

$ snap version
snap 2.16+ppa70.d7db7888-1
snapd 2.16+ppa70.d7db7888-1
series 16

(released ubuntu core image)