Fix uninitialized constant during rpmbuild with unknown modules_dir

http://koji.katello.org/koji/getfile?taskID=73464&name=build.log

<pre>
/usr/lib/ruby/gems/1.8/gems/kafo-0.3.7/lib/kafo/puppet_module.rb:50:in `parse': uninitialized constant Kafo::PuppetModule::ConfigurationException (NameError)
	from /usr/lib/ruby/gems/1.8/gems/kafo-0.3.7/lib/kafo/configuration.rb:71:in `modules'
	from /usr/lib/ruby/gems/1.8/gems/kafo-0.3.7/lib/kafo/configuration.rb:71:in `map'
	from /usr/lib/ruby/gems/1.8/gems/kafo-0.3.7/lib/kafo/configuration.rb:71:in `modules'
	from /usr/lib/ruby/gems/1.8/gems/kafo-0.3.7/bin/kafo-export-params:84:in `print_out'
	from /usr/lib/ruby/gems/1.8/gems/kafo-0.3.7/bin/kafo-export-params:34:in `execute'
	from /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/command.rb:67:in `run'
	from /usr/lib/ruby/gems/1.8/gems/clamp-0.6.2/lib/clamp/command.rb:125:in `run'
	from /usr/lib/ruby/gems/1.8/gems/kafo-0.3.7/bin/kafo-export-params:129
	from /usr/lib/ruby/gems/1.8/bin/kafo-export-params:19:in `load'
	from /usr/lib/ruby/gems/1.8/bin/kafo-export-params:19
rake aborted!
</pre>

The modules_dir didn't exist, causing an error of some sort and then the error handler hit this bug.  I haven't verified this fix though.