Moved enable/disable download buttons code to a generic method.

Changed code to enable/disable Download buttons on Reports tab in Utilization explorer. Buttons were not getting enabled/disabled based upon result data when user sent up tree_select transaction while user was on Reports tab. Existing code was only handling enable/disable of download buttons when switching tabs.

https://bugzilla.redhat.com/show_bug.cgi?id=1113062
https://bugzilla.redhat.com/show_bug.cgi?id=1114659

@dclarizio please review/test