Improvements to resolv.conf handling in the chroot

Minor changes in how resolv.conf is managed between Ubuntu's precise and
quantal releases were causing failure when building with quantal images.
Making a tweak to cp's behavior deals with both cases effectively.

In the event that resolv.conf is a dangling symlink, care is taken to ensure
the symlink target dir exists before employing the POSIXLY_CORRECT cp.

I was able to successfully build a precise and quantal AMI after making these changes.