Possibility to add more options to the SSH and SCP commands

[oEscal]

When using this library to create Juju charms used in my OSM's VNFs, I felt the need to use other options for the SSH connection. For instance, I couldn't do so, if I had to use the SSH client option ServerAliveInterval, because there is not an argument on the run or ssh functions of the SSHProxy class to pass these SSH client options.

Therefore, the modifications I introduced now allow a developer to add these options that might be useful/needed in some specific cases. For example, if I now have the following code:

from osm.sshproxy import SSHProxy

ssh_proxy = SSHProxy('controller', 'ubuntu')
ssh_proxy.run('sudo apt install', ssh_options=['ServerAliveInterval=5', 'ConnectionAttempts=1'])

The corresponding ssh function will produce the command, with this set of wanted options:

['sshpass', '-p', '', 'ssh', '-i', '/var/lib/juju/agents/.ssh/id_sshproxy', '-o', 'StrictHostKeyChecking=no', '-o', 'ServerAliveInterval=5','-o', 'ConnectionAttempts=1', '-q', 'ubuntu@controller', 'sudo', 'apt', 'install']

Note: I also added this possibility to the scp function.