Use --numeric-owner when extracting base image

When extracting the base image without --numeric-owner, user and group
names in the tarball are mapped to uid/gid by the host.  This can cause
problems when building an image for some other distro than you're
running yourself.  For example, building an Ubuntu image on openSUSE
ends up with /var/cache/man in the image owned by 'proxy' (uid 13)
instead of 'man' (uid 6), because the host (openSUSE) uses uid 13 for
the 'man' user.  This particular man/proxy discrepancy results in
"fopen: Permission denied" errors when apt-get does its "Processing
triggers for man-db" thing in the Ubuntu system.  I wouldn't be
surprised if there were other kinks caused by this uid/gid mapping
discrepancy too, but that's the one I found so far.

The same thing can also happen with Fedora, but seems to be less likely,
or at least less obvious to me when building Fedora images on openSUSE.
But, IMO, it's better to be safe and just use --numeric-owner on all
base image untarring outside the chroot.

Change-Id: I9da5ac66dd182e7278fe4fee932093f61d35673a
Merge "Use --numeric-owner when extracting base image"