Make sure VM image dir exists
Make sure VM image dir exists

When moving the VM image directory to XDG_CONFIG_DIR, I removed an
ensure_directory() call that should have been kept. This results in
the 'images' subdirectory of XDG_CONFIG_DIR/gnome-boxes not being
created, which then causes VM creation failures on "new" systems.
This should fix bug #668536.

vbenes/gnome-boxes,vbenes/gnome-boxes