Split out installation of packages from customize_rootfs into a separate script.

Split out installation of packages from customize_rootfs into a separate script.

The build_image script now calls install_packages.sh followed
by customize_rootfs.sh.

The current system installs packages and performs customization
fixups from within the rootfs it is building. In order to
cross-build properly we'll need to do these steps from outside
of the root. Splitting package installation and rootfs customization
will make it easier to do this. A follow-on change will modify
customize_rootfs to run from outside of the rootfs.

Committed: http://chrome-svn/viewvc/chromeos?view=rev&revision=300

[Bill Richardson, 2009-11-20 21:55:13]

LGTM