Now using POSIXLY_CORRECT cp for resolv.conf

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.
Forgot to finish writing a comment ><
Hack to add an ephemeral image to generated AMI