AttributeError when no Physical Drive serial returned

[Vil Surkin]

Sometimes idrac doesn't know physical drive serial number (in my case it is H730 ctl and Crucial CT960M50 SSD). If so, `list_physical_disks()` definition throws an exception:

```
Traceback (most recent call last):
  [ ... ]
  File "../venv/lib/python2.7/site-packages/dracclient/client.py", line 324, in list_physical_disks
    return self._raid_mgmt.list_physical_disks()
  File "../venv/lib/python2.7/site-packages/dracclient/resources/raid.py", line 200, in list_physical_disks
    for disk in drac_physical_disks]
  File "../venv/lib/python2.7/site-packages/dracclient/resources/raid.py", line 227, in _parse_drac_physical_disk
    'SerialNumber'),
  File "../venv/lib/python2.7/site-packages/dracclient/resources/raid.py", line 235, in _get_physical_disk_attr
    drac_disk, uris.DCIM_PhysicalDiskView, attr_name)
  File "../venv/lib/python2.7/site-packages/dracclient/utils.py", line 61, in get_wsman_resource_attr
    return item.text.strip()
AttributeError: 'NoneType' object has no attribute 'strip'
```

[Anish Bhatt (anish7)]

Hit this one as well, will submit fix.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/389368

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/389368
Committed: https://git.openstack.org/cgit/openstack/python-dracclient/commit/?id=5804c28b5f13fc7637a2b0216c05a8ed6476929c
Submitter: Jenkins
Branch: master

commit 5804c28b5f13fc7637a2b0216c05a8ed6476929c
Author: Anish Bhatt <email address hidden>
Date: Mon Sep 26 23:10:49 2016 -0700

    Raid controller and Physical Drive attributes need to be nullable

    This can fail with
    AttributeError: 'NoneType' object has no attribute 'strip'
    otherwise

    Closes-Bug: #1550328
    Change-Id: I8eafe606407cddc1e9ea03a33473b65ff3b59384

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/394465

[OpenStack Infra (hudson-openstack)]

Related fix proposed to branch: master
Review: https://review.openstack.org/394466

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/394510

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/394465
Committed: https://git.openstack.org/cgit/openstack/python-dracclient/commit/?id=ba1eb4aa99db7b78168ff2b0d19918924a0cb2aa
Submitter: Jenkins
Branch: master

commit ba1eb4aa99db7b78168ff2b0d19918924a0cb2aa
Author: Dmitry Tantsur <email address hidden>
Date: Mon Nov 7 15:36:04 2016 +0100

    Raise a reasonable error on non-nullable flags with empty text

    Now it fails with AttributeError: 'NoneType' object has no attribute 'strip'.
    Raise a new exception with proper explanation instead.

    Partial-Bug: #1550328
    Change-Id: Ie9f9d212c934bb75e8224dd64ec8df7f788b86d3

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/394466
Committed: https://git.openstack.org/cgit/openstack/python-dracclient/commit/?id=aeebdf890bfc25d42a8df8958f36c3347252c0a8
Submitter: Jenkins
Branch: master

commit aeebdf890bfc25d42a8df8958f36c3347252c0a8
Author: Dmitry Tantsur <email address hidden>
Date: Mon Nov 7 15:47:44 2016 +0100

    Raise a specific exception instead of generic AttributeError

    Currently we raise an AttributeError when expected attribute is missing
    from the response. This is not very developer-friendly, so this patch
    creates a new exception (derived from AttributeError for compatibility)
    for this purpose.

    Change-Id: If2ac03dcd410d451dc7bbfe7bbd0b145da201c9a
    Related-Bug: #1550328

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/394510
Committed: https://git.openstack.org/cgit/openstack/python-dracclient/commit/?id=4fbea94a1c0ccf7ca4ab3416f2949975d9fc3077
Submitter: Jenkins
Branch: master

commit 4fbea94a1c0ccf7ca4ab3416f2949975d9fc3077
Author: Dmitry Tantsur <email address hidden>
Date: Mon Nov 7 15:55:47 2016 +0100

    Make name and description nullable for virtual disks

    This change fixes inspection failure on my hardware.
    In the future we should develop a better understanding on which
    fields are mandatory and which are not, as right now we're very
    inconsistent with handling them.

    Change-Id: Ia2af90fec4eef168953552a947933617e7c808d0
    Closes-Bug: #1550328