FakeResponse: use a default status code

When running some tests from test_restapi.py, the following error happens:

    TypeError: unorderable types: NoneType() < int()

In Python 2, comparing NoneType and integers is possible:

    >>> None < 2
    True

But in Python 3, it's not allowed. Fix this by using a default status code.

Change-Id: Ic0fad5c68f3bf2dd8a2b98423549903f982192c9
Merge "FakeResponse: use a default status code"