Make integration tests py.testable

These changes make tests in soco_unittest runnable via py.test. I have not touched the code in execute_unittests.py, which is still usable. But if you want to use py.test, you can do this in the root directory

```sh
py.test -m "integration" --ip XXX.XXX.XXX.XXX
```

will run just the integration tests

```sh
py.test -m "not integration"
```
 will run everything *except* the integration tests, and

```sh
py.test  --ip XXX.XXX.XXX.XXX
```

will run everything