stream: avoid hitting network by providing default error response
stream: avoid hitting network by providing default error response

Tests were failing on my laptop running OSX as requests were running
for a long time trying to talk to an actual device at 192.168.100.1.
This change avoids hitting the network by providing a response for
the requests made by the library.

digidotcom/python-wvalib,digidotcom/python-wvalib