disk-image-create: fix test when no argument is given.

Avoid a warning when multiple arguments are passed to disk-image-create
like:

bin/disk-image-create: 146: [: aa: unexpected operator

Change-Id: I619d7bf2e4b56885d629019b80b249bc80b8f43e
Remove use of sudo from yum pre and post elements

sudo is not needed, since in-chroot elements are run in the context
of the root user. Furthermore, sudo in pre-install is problematic as
sudo may not have been installed yet (imagine a debootstrap build)

Change-Id: Ib5c7e176a90fe3b8fa9c3cd702d3d815df54f472
Merge "disk-image-create: fix test when no argument is given."
Merge "Remove use of sudo from yum pre and post elements"