(RAZOR-362) Remove saucy from build defaults

This commit removes saucy from build_defaults. It went EOL on July 17,
2014
Fix Trusty's preseed file's url to squashfs

The previous squashfs file was pointing to a local file path on the razor
server, rather than a URL to that file.

Fixes https://tickets.puppetlabs.com/browse/RAZOR-365