[LTP] Make FTP test compatible with Busybox and Dropbear.

[Köry Maincent]

Hello,

I am working with LTP on an embedded board.
I would like to notice the rhost_run command does not work with Dropbear ssh
client. I am trying to understand how tst_net work but I am a bit struggling
with it. What is the usage of TST_USE_NETNS, and the purpose of netspace (it
seems to be used to configure a virtual interface)?
My aim was to make FTP test work with Dropbear and Busybox. If someone could
point me out how to do it.

Regards,

Köry