Replace "mount -o loop" with explict losetup use in build_image.

Replace "mount -o loop" with explict losetup use in build_image.

This fixes the loop device leak. The problem is that inside the chroot, we
have /etc/mtab as a symlink to /proc/mounts. That works most of the time,
but if you mount something using "-o loop", it isn't cleaned up correctly
when you umount it. To avoid that, we either have to replace the /etc/mtab
symlink with an empty file when we create the chroot, or we have to make
sure that we never execute a "mount -o loop" command from within the chroot.
If we use an empty /etc/mtab file, the builds work fine, but then we can't
see any mounted partitions that the host creates outside the chroot (such as
USB keys), which causes other problems. Bleah.

[adlr, 2010-04-08 18:22:25]

LGTM w/ comment

http://codereview.chromium.org/1594020/diff/1/2
File src/scripts/build_image (right):

http://codereview.chromium.org/1594020/diff/1/2#newcode131
src/scripts/build_image:131: sleep 1  # me belong cargo
write a better comment?

[Bill Richardson, 2010-04-08 18:23:47]

http://codereview.chromium.org/1594020/diff/1/2
File src/scripts/build_image (right):

http://codereview.chromium.org/1594020/diff/1/2#newcode131
src/scripts/build_image:131: sleep 1  # me belong cargo
On 2010/04/08 18:22:26, adlr wrote:
> write a better comment?

I *knew* you'd say something about this!