Detect rsync remote connection using colon

I updated ``FileSyncTask`` so it can detect remote connection w/o specification of user in ``destinationDir`` or ``sourceDir``.
According to rsync manual, they both can be in the following formats: ``[USER@]HOST:SRC,
[USER@]HOST::SRC,
[USER@]HOST:DEST,
[USER@]HOST::DEST``
As we can see, "USER@" part is optional.