This adds a transport that uses /usr/bin/ssh calls to communicate
with remote hosts.
This transport is a bit slower and buffers output more than paramiko,
so it is only used if paramiko is not available, or forced with an
environment variable.
https://fedorahosted.org/freeipa/ticket/3890
This will make it possible to use a different mechanism for cases like
- Paramiko is not available
- Hosts without SSH servers (e.g. Windows)
Add BaseHost, Transport & Command base classes that define the interface
and common functionality, and Host, ParamikoTransport & SSHCommand with
specific details.
The {get,put}_file_contents methods are left on Host for convenience;
all other Transport methods must be now accessed through the transport.
Part of the work for https://fedorahosted.org/freeipa/ticket/3890
