Refactor of SSH client

* Override Paramiko's SSH client to return status code
* Created strongly typed response for exec_command
* Created new base SSH client which handles the bare essentials
* Created base SSH behaviors to encapsulate functionality from the client
* Updated remote instance client to work with updated SSH client

Change-Id: Ieb0374264608ead5ae9e4dab4c8c912404d54333
Merge "Refactor of SSH client"