Add yum element.

The yum element provides for specific customizations
for yum based distros.  The included customization is
a yum cache mounted outside of the chroot so that yum
downloaded packages are reused on subsequent image builds.

Change-Id: I6833c9fdbc83cb09debec6a789082e105c917800
Package dib-run-parts

dib-run-parts is a symlink into the elements directory.

During packaging the symlink is preserved however
during installation dib-run-parts becomes a file containing
the contents of the symlink target.

Related-Bug: #1212482
Change-Id: I78c28a52689810a2ccfc9925a9ac8df017c44326
Update stackforge references to openstack

Change-Id: I17e896eddf6fe84f4784cac8231552ee3d21aa39
Set file permission to be executable.

When ramdisk-image-create is called with the hwdiscovery element,
it failed to install hwinfo package.

The root reason is 10-hwinfo is not executable, the fix is to
set the file permission of 10-hwinfo to be executable.

Change-Id: I3a57147103f607b3975eb6ad23a44475f26c2f1e