localboot element doesn't work for ubuntu image

[Zhenzan Zhou]

When creating an ubuntu image with localboot, the postinst script of grub-pc will try to find root device and install grub which will definitely fail in such a chroot environment. Here is the log:

Setting up grub-pc (2.02~beta2-9ubuntu1) ...

Creating config file /etc/default/grub with new version
grub-probe: error: cannot find a device for / (is /dev mounted?).
grub-probe: error: cannot find a device for /boot (is /dev mounted?).
grub-probe: error: cannot find a device for /boot/grub (is /dev mounted?).
/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).
dpkg: error processing package grub-pc (--configure):
 subprocess installed post-installation script returned error exit status 1
Processing triggers for libc-bin (2.19-0ubuntu6.6) ...
Errors were encountered while processing:
 grub-pc
/bin/df: cannot read table of mounted file systems: No such file or directory
E: Sub-process /usr/bin/dpkg returned an error code (1)

[Marios Andreou (marios-b)]

review @ https://review.openstack.org/#/c/168208/2 (not sure why isn't auto linked here)

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/168208
Committed: https://git.openstack.org/cgit/openstack/tripleo-image-elements/commit/?id=476af257304f42f3e1521919c7b6e06d94d07911
Submitter: Jenkins
Branch: master

commit 476af257304f42f3e1521919c7b6e06d94d07911
Author: Zhenzan Zhou <email address hidden>
Date: Fri Mar 27 10:28:26 2015 +0800

    Fix ubuntu grub-pc install failure

    When creating an ubuntu image with localboot, the postinst script
    of grub-pc will try to find root device and install grub which will
    definitely fail in such a chroot environment.

    Closes-Bug: #1437548
    Change-Id: Ia29387f33c33e760c2711c687a43025b2013bd84