fix undefined local variable,definition_dir

Specifying an non writeable definition dir returned an undefined variable error rather than the helpful error message.
Running unnecessary media check every time

Skips to Install Fedora 20
from default
Test this media & install Fedora 20
Merge pull request #893 from braddeicide/master

Enable "DefinitionDir not writable" error msg, skip Fedora 20 media check.