ch-builder2tar -b ch-image: shows internal path

e.g.:

$ ch-builder2tar -b ch-image spack/centos7 .
builder: ch-image
exporting
/var/tmp/reidpr/ch-image/img/spack%centos7
 596MiB 0:00:01 [  <=>                                                         ]
compressing
 596MiB 0:00:06 [============================================>] 100%
-rw-r----- 1 reidpr reidpr 192M Mar 17 10:25 ./spack%centos7.tar.gz

We don't want to be advertising ch-image storage directory paths in non-debug output (here /var/tmp/reidpr/ch-image/img/spack%centos7).