rtrclient: replace ssh public key parameter with host key
rtrclient: replace ssh public key parameter with host key

It's not required anymore to specify a SSH public key for a connection.

Instead of a public key the path to the host key can passed as last
argument (optional).
If it's provided the authenticity of the host is verified.

rtrlib/rtrlib,rtrlib/rtrlib,rtrlib/rtrlib