logilab-devtools #6443 lgp build: explain why vbuild fails [rejected]

If vbuild fails building the package, there is no information about why the build failed:

alf@crater:~$ ~/dev/public/logilab/devtools/bin/lgp build --distrib hardy ~/dev/public/logilab/devtools
I:logilab.devtools.lgp.build: Cleaning repository...
I:logilab.devtools.lgp.build: Use '/home/alf/dist/logilab-devtools-0.12.0.tar.gz' as original source archive (tarball)
I:logilab.devtools.lgp.build: Creation of the debian source package in '/tmp/tmpI4cOMo/logilab-devtools-0.12.0'
I:logilab.devtools.lgp.build: Building dsc file: logilab-devtools_0.12.0-1.dsc
I:logilab.devtools.lgp.build: Building debian package for distribution 'hardy' and arch 'amd64'
C:logilab.devtools.lgp.build: Command '['vbuild', '-d', 'hardy', '-a', 'amd64', '--result', '/home/alf/dist/hardy', '/tmp/tmpI4cOMo/logilab-devtools_0.12.0-1.dsc']' returned non-zero exit status 1

In this case, this is because devtools build depends on debhelper >= 7 which is not available in hardy, but I had to rerun vbuild manually to get the pbuilder logs and understand what was wrong.

appeared in<not specified>
done in0.12.2
load left0.000
closed by<not specified>