Add option for user to specify ssh binary name.

[cr1901]

This is mostly useful for smaller embedded Linux systems that may only have dropbear/dbclient installed, without needing to do a sed replace!

[laurent22]

I'd expect these alternative clients would be symlinked to ssh?

[cr1901]

@laurent22 You would think, but on this machine in question (Tinkerboard running DietPi), they are not I'm afraid. I know at least one upcoming board from the J Core Project will have the same problem.

wjones@DietPi:~$ which ssh
wjones@DietPi:~$ which dbclient
/usr/bin/dbclient
wjones@DietPi:~$

Yes, I can create a symlink b/c I have sudo privileges, but this is meant for people who can't.