Switch to 'mapped' access mode for hostfs

Passthrough mode only works as expected when running as root. On
Debian/Ubuntu systems qemu runs as user 'libvirt-qemu' and group 'kvm'
so all shared files must be chowned to grant access from guests.

Symlinks created on the host are still problematic because the Plan 9
filesystem has no direct notion of symbolic links, see [1].

[1] - http://ericvh.github.com/9p-rfc/rfc9p2000.u.html

testing/make-testing

@@ -4,6 +4,7 @@ DIR=$(dirname `readlink -f $0`)
 . $DIR/testing.conf
 
 rm -f $LOGFILE
+mkdir -p $BUILDDIR
 
 if [ $ENABLE_BUILD_BASEIMAGE = "yes" ]
 then