Fix the issue with defining FTP log depot.

The method connect_ftp has been deleted when some of the logic have been moved from LogFile into FileDepot and its subclasses. 
Consequently the FTP log depot validation failed.

https://bugzilla.redhat.com/show_bug.cgi?id=1151173
@lfu I don't know why this is here...  The correct case statement to change should be here: https://github.com/ManageIQ/manageiq/blob/master/vmdb/app/controllers/ops_controller/diagnostics.rb#L135

I think this ```when``` can be deleted.  @h-kataria is that correct?