Allow specify a name when uploading flist

[zaibon]

I found out that when uploading a flist to the hub. The filename is used to name the flist in the hub. This seems ok but I also found that some name get somehow changes during upload.

example: I have a file called zos:0.1.0-rc2.flist but once it is uploaded to the hub, it's name is zos0.1.0-rc2.flist. So the : get removed.
Maybe there is technical reason for I'm not sure. But if we would add a flag --name then we could decouple the file name with the actual flist name in the hub