(#5927) Change Reports urls to be relative with use of ActionController::Base.relative_url_root setting

when installing puppet dashboard in a different path then the root url (e.g http://\<host\>/puppet-dash/ ), when accessing the Reports, the link will redirect back to /reports instead of \<different path\>/reports (e.g http://\<host\>/reports instead of http://\<host\>/puppet-dash/reports) and will return a 404. this fix prepend the ActionController::Base.relative_url_root  to the Reports href and therefor return the correct url.