Revert "Pin to rake < 10.2.0 on Ruby 1.8"

This reverts commit cefa44cfbb37970f26a7136a2a3234ba9e7e9639.
Treat puppet-lint warnings as failures
We download and install discovery images
non string parameters allowed
Quoted osfamily-case-statement

Since Puppet 3.5.x options in osfamily-case-statements have to be quoted
more quotes around case statements
Fix TFTP module dependency