apport-retrace: give proper error message when installArchives() fails

So it could not install the dbgsyms completely it seems. It should give a more friendly error message.

However, please note that you should use -u if you use apport-retrace on a production system.

 apport (0.81) gutsy; urgency=low
 .
   * apport/report.py: Remove '[apport]' default bug title prefix. (LP: #94819)
   * apport/crashdb_impl/launchpad.py: Tag new bugs with
     'apport-<problemtype>'. This replaces the former '[apport]' prefixing.
   * debian/local/setup-apport-retracer: Specify a path in '.' command and
     use sh again. Yay for me needing three attempts before actually RTFMing
     how '.' works (which is really nasty and strange IMHO).
   * bin/apport-chroot: Fix symlinks before repackaging the chroot tarball in
     'install' and 'installdeb' modes.
   * debian/local/setup-apport-retracer: Install python-libxml2 and python-apt.
   * bin/launchpad-crash-digger: Supply --auth instead of the deprecated
     --cookie to apport-chroot.
   * bin/apport-chroot: Fix identifier name in command_retrace().
   * debian/local/setup-apport-retracer: Set APPORT_CRASHDB_CONF to the local
     crashdb.conf.
   * bin/apport-chroot: Unset APPORT_CRASHDB_CONF for login and retrace.
   * bin/launchpad-crash-digger: Check the release of a bug and whether we have
     a chroot for it before untagging it. This avoids loosing tags for bugs we
     do not yet have a working retracer chroot for.
   * bin/apport-retrace: Do not abort with an exception if package installation
     fails. Give a proper error message instead and point to -u. (LP: #115681)
   * apport/crashdb_impl/launchpad.py, update(): Create a temporary directory
     and use proper file names for the new attachments. With TemporaryFile(),
     attachment file names ended up as '<fdopen>'. (LP: #115347)
   * apport/report.py, add_os_info(): Add field 'NonfreeKernelModules' which
     lists loaded kernel modules which do not have a FOSS license. This is
     particularly helpful for quickly checking for restricted graphics drivers.
     (LP: #103239)
   * apport_python_hook.py: Move the apport.* imports into the try: block and
     move the likely_packaged() test to the top, to avoid importing
     apport.report and creating a Report object for non-packaged scripts. This
     makes the entire code more efficient and robust against errors in the
     apport modules. (LP: #109955)
   * apport/report.py, add_gdb_info(): Intercept OSError from gdb invocation
     (which might be segfaulting itself) and just do not put any gdb output
     into the report. The automatic retracers can try their luck again.
     (LP: #112501)
   * bin/apport-retrace: Fix handling of packages which are still known to
     /var/lib/dpkg/status, but do not have an apt record any more; treat them
     like virtual packages and just issue a warning instead of falling over.
     (LP: #107474)