Fix usage of NexusPortBindingNotFound exception

Currently the required keyword argument (port_id)
is not passed when the exception is raised. In fact
this exception has never been raised before due to
another bug (1173131) so this change also has to
ensure it doesn't break any existing code using
functions which can possibly raise this exception.

Fixes bug 1174323.

Change-Id: I81f0b0def7db163fb0fbb5e03be511113c8d0be5
Merge "Fix usage of NexusPortBindingNotFound exception"