(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
Ubuntu Precise task encounters error

On Ubuntu Precise, the error: "mirror does not support the specified release"
occurs. Turns out this is due to a change to how the preseed file is fetched.
Trusty works fine with the current config, so this will change Lucid and
Precise back to the last working version.

This commit follows the decision that the base task should be kept most
up-to-date, meaning that `ubuntu.task` should currently mimic Trusty.

Fixes https://tickets.puppetlabs.com/browse/RAZOR-366