hyperv: remove get_console_output method

The get_console_method() in the hyperv driver only logged a debug
message and returned an empty string.  It seems like much better and
expected behavior to not implement the method at all so that a
NotImplementedError is raised.  This will properly propagate back
through the API.  Not Implemented is certainly different to the user
than telling them their console output is always empty.

Change-Id: I9df81a74ac533a73f30305f3eb12a8ff7608b293
Merge "hyperv: remove get_console_output method"