push_firmware: - use ftp command only for linux
 - use ncftp if available
 - lower sleep for Alice telnet session, add sleep after QUIT
 - only split image if greater than 7808k
 - hide output of some commands
 
refs #2113

git-svn-id: file:///var/svn/freetz/trunk@11821 149334a1-2f27-0410-a3b9-fc62619ac1e6