Improve some of the comments.
@core is already implied

No need to specify it again
More comments.
Don't cripple IPv6
Turn off daemons from launching.

First boot setup (such as sshd setting up keys) and logging will
be delayed until Vagrant boots the box.
Comment cleanup
Split the transaction off as a shell command
Unmount the CDROM when we're done with it
More housecleaning bits.

Removing the yum cache saves about 40 MiB. Just removing
everything in the /tmp/ directory as a 'why not'.
Email the results of the build.