The virt driver FakeDriver used in both the functional and in the unit
test used a global state to configure the host and node names the driver
reports. This was hard to use when more then one compute service is started.
Also global state is dangerous.
It turned out that only a set of unit tests are using multiple nodes per
compute the rest of the tests can simply use host=<hostname>,
nodes=[<hostname>] setup.
So this removes the global state.
Change-Id: I2cf2fcbaebc706f897ce5dfbff47d32117064f9c
b5666fb492