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
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
