Enable logging of subprocess output

In the original approach, it was impossible to monitor the
progress of a subprocess because all of the stdout/stderr was
being buffered for retrieval only after the process exited.

With this patch, we will now drop stdout into log.debug1() and
stderr into log.error() as they come in (in addition to storing
the complete results for retrieval later). This will make
debugging efforts much simpler.
DBusRole: New method get_name, using in RoleD.getNamedRole

Fixes https://fedorahosted.org/rolekit/ticket/3

Bugs closed: 3

Reviewed at https://reviewboard-fedoraserver.rhcloud.com/r/55/
Improve exception logging

There are several places where we simply log an exception without
any context. This patch adds the exception type to these messages
to improve debugging.
Domain Controller deployment
Make decommission asynchronous
Domain Controller: Add decommission routine