add file, ssh.py

Change-Id: I5f732811e458cd6f901d09021862bce0b8e54075
Implements: blueprint ssh-module
Implement class SSH to layout ssh-module

Defines the following SSH instance methods:
    * connect()
        Creates an ssh connection and prefers ssh keys.
        Uses proxy if defined.
    * remote_execute()
        Connects, executes command, and disconnects.
        Attempts to respond to password prompts if
        sudo commands are issed by a sudoer who does
        not have passwordless sudo.
    * _get_proxy_socket()
        Returns a CommandProxy instance built from the
        current SSH instance attributes. Is then
        used when connecting to target host as in:

            proxy = connect(<host>)
            client = connect(proxy=proxy)

Change-Id: I9e5f3463cfa1bdd275b6be38e3f6c37ba3d717f8
Implements: blueprint ssh-module
add test_connection() method

Returns True on success, Fail otherwise.

Change-Id: I4b8171fe1cbcd5af47bc3e6c7557cee917d69d7c
Implements: blueprint ssh-module
add shorcut method to create an SSH instance

function connect():
    - provides a module-level shortcut
    - formats TypeErrors in the context
      of connect(), rather than appearing
      to be from __init__
classmethod get_client():
    - returns an instance of its class

Change-Id: I95e7aec00e307ea80d4e7d719f61b5dc300bfc7d
Implements: blueprint ssh-module
implement platform_info instance property

returns a list which describes the target host's
    - distro
    - version
    - architecture

Change-Id: I801fca848141ae59cb46754cf80e2db7ea6cc391
Implements: blueprint ssh-module