ftp: wait for 60 seconds for connection Close then declare it dead
ftp: wait for 60 seconds for connection Close then declare it dead

This helps with indefinite hangs when transferring very large files on
some ftp server.

Fixes #2912

ncw/rclone,ncw/rclone,olihey/rclone,B4dM4n/rclone,olihey/rclone,ncw/rclone,B4dM4n/rclone,olihey/rclone,ncw/rclone,B4dM4n/rclone,B4dM4n/rclone,olihey/rclone