Fix 'os-interface' resource name for Nova V2.1

V2 and V3 diff for this resource name is below-
V2 - '/servers/os-interface'
V3 - '/servers/os-attach-interfaces'

V3 resource name needs to be changed to work that for V2.1

Change-Id: I37bd7cee7e8879b01a8aee739d74c2dd6e033dc4
Closes-Bug: #1368035
Merge "Fix 'os-interface' resource name for Nova V2.1"