Add get_attr for EXTED_PLURALS

FW Client CLI change (d04f3822b5b7ef8d6c918c753a6e7733bdda0344)
breaks nova unit test.
The change itself is good, but we should change nova ut before
the changing neutron client.
In this commit, we will skip the error adding get_attr
for the property.
Note, this is a temporary fix, we will revert this change
when Nova side unit test fixed

Fixes bug 1209364

Change-Id: I6b5d7e6d529e05c89ad14c09069f4651ef3a500e