KNL-1165 Improve error handling in ReEncryptPasswords.

This improves the error handling when properties aren't defined in the configuration and also allows the loading of the files to be configured through system properties.

git-svn-id: https://source.sakaiproject.org/svn/kernel/trunk@134160 66ffb92e-73f9-0310-93c1-f5514f145a0a