drive: work around drive bug which didn't set modtime of copied docs
drive: work around drive bug which didn't set modtime of copied docs

Google drive appears to no longer be copying the modification time of
google docs.

Setting the mod time immediately after the copy doesn't work either,
so this patch copies the object, waits for 1 second and then sets the
modtime.

Fixes #4517

ncw/rclone,ncw/rclone,ncw/rclone,ncw/rclone