CA-142451: Unit tests

Covering changes related to CA-142451.

Signed-off-by: Flavien Quesnel <flavien.quesnel@citrix.com>
Maybe create an assertDevicePath method:

```python
...
        self.assertPath(self.node1, iscsi_sr.path)
        self.assertEquals(node1_ip_port, iscsi_sr.tgtidx)
        self.assertEquals(node1_ip_port, iscsi_sr.address)
...
```

After that these 3 could be moved to one assertion:

```python
        self.assertActiveNode(node1, iscsi_sr)

```