Fixed errors in tests and provisionLink method.

SDNNetwork model is supossed to store the mapping between the OpenflowSwtichResource id and its floodlight id to provision the internal links. But since there's no way to put this information into model right now, the pull request introduces a work around, which is

1) Getting the resource from the resource model, using the deviceName (s2, s3, etc)
2) Calling allocateFlow from this resource.
3) The OpenflowSwitch resource model contains the swtichId, so there's no information lost.

In the future, we should develop a way to store this information in the SDNNetwork model.