Relax schema validation on backendconfiguration (#2258)

* Relax schema validation on backendconfiguration

The schema validation for backendconfig was set too tightly and it was
rejecting valid responses from the backend API. This potentially causes
issues when running against the api. This commit addresses this by
changing the schema validation to ensure that we properly validate the
response received by the backends and no longer reject valid responses
moving forward.

* Add changelog

* Fix tests and lint

CHANGELOG.rst

@@ -20,6 +20,12 @@ The format is based on `Keep a Changelog`_.
 `UNRELEASED`_
 =============
 
+Fixed
+-----
+
+- A potential issue where the backend configuration schema validation would
+  improperly reject valid responses from the API (#2258)
+
 `0.7.1`_ - 2019-03-04
 =====================
 

qiskit/providers/models/backendconfiguration.py

@@ -7,7 +7,7 @@
 
 """Model and schema for backend configuration."""
 
-from marshmallow.validate import Equal, Length, OneOf, Range, Regexp
+from marshmallow.validate import Length, OneOf, Range, Regexp
 
 from qiskit.validation import BaseModel, BaseSchema, bind_schema
 from qiskit.validation.fields import Boolean, DateTime, Integer, List, Nested, String
@@ -47,7 +47,7 @@ class BackendConfigurationSchema(BaseSchema):
     local = Boolean(required=True)
     simulator = Boolean(required=True)
     conditional = Boolean(required=True)
-    open_pulse = Boolean(required=True, validate=Equal(False))
+    open_pulse = Boolean(required=True)
     memory = Boolean(required=True)
     max_shots = Integer(required=True, validate=Range(min=1))
 
@@ -56,7 +56,7 @@ class BackendConfigurationSchema(BaseSchema):
     sample_name = String()
     coupling_map = List(List(Integer(),
                              validate=Length(min=1)),
-                        validate=Length(min=1))
+                        validate=Length(min=1), allow_none=True)
     n_registers = Integer(validate=Range(min=1))
     register_map = List(List(Integer(validate=OneOf([0, 1])),
                              validate=Length(min=1)),