Enhance test libraries for use with various deployments

Currently, the voltha-atest-provisioning test libraries have functions that are usable with a local voltha deployment. It would be nice to enhance that so that we can use these functions on voltha deployments on remote servers (i.e full SEBA physical pod). 

The seba tests can leverage some of these functions. Mainly, the "send_command_to_voltha_cli" function. But its hardcoded right now log into voltha "@localhost". We should extract this to be an argument in the function itself. Likewise, with the "send_command_to_onos_cli"