rootfs_*.bbclass: List which post-install scripts can not be run

rootfs_*.bbclass: List which post-install scripts can not be run

When preping a read-only rootfs and finding some post-install
scripts that can not be run, list the names of said scripts to
avoid having to look around the rootfs to find a list.

Signed-off-by: Jeffrey C Honig <jeffrey.honig@windriver.com>
Signed-off-by: Jeff Polk <jeff.polk@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>