CoraidDriver: do not call login from __init__

We should not call _login from the driver's __init__.
If the ESM is down, the constructor will fail.

- self._login()

Fixes bug 1157500

Change-Id: Ie57fbb6d3704d270a81cd9eb056d7988989da1f8
(cherry picked from commit 28102bc54ac2793ea17f47c81f6812bb84615834)