commands: add host key: now supports adding ssh-rsa keys

before it suported only RSA PEM pubblic key, now if the user input a
ssh-rsa key (which is different from PEM format) it converts the key
into pem format
commands: created a method setKey in VMContro and moved the key handling there
commands: updated open console and list macs to the getKey method
pylib: add support for ssh-agent

the client side libraries to talk with airboss now can use
ssh-agent if the variables are defined.

At the moment only RSA keys are supported no DSA