Not helpful error message when binding fails

[Mohammad Banikazemi]

When the vif type is detected as binding_failed, log a better error message that indicates the reason for not being able to complete plunging the vif in Kuryr.

[Mohammad Banikazemi (mb-s)]

Kuryr tries to execute the binding_find shell script that does not exist. We could check for this vif type and avoid attempting to execute the non existing script and return a better error message.