SFTP support for Roborock

[Lanchon]

requirement: armv7l roborock firmware based on ubuntu 14.04.

howto: download this archive to /mnt/data and extract it, then run sftp/install.

motivation: scp is not a remote filesystem protocol, and fish (files over shell) is long deprecated and unsupported in gnome. sftp://root@rockrobo is supported natively in nemo, nautilus, thunar, etc. most remote file managers, such as filezilla, also support sftp. i could not find a single linux GUI for scp.

[Lanchon]

@dgiese, it'd be great if the sftp-server binary could be added to dustbuilder... please? :)

[Lanchon]

come to think about it, adding overlayfs to dustbuilder would be even better!

[Lanchon]

so big surprise: the kernel is lacking the overlay support :(... this means too much hacking to make it work. an easier alternative would be bind mounting all around a-la Magisk.

bind mounts could provide all non-essential functions, such as DNS hacking for valetudo and SSH keys, while fw images would just need to provide root access via custom adbd. this way fw images could be shared among users and would no longer need to be custom-built for each user.

[Lanchon]

btw... please please please consider adding sftp to dustbilder: it is a single 50 KiB file.

pretty please?