Set status code to 500 for "generic" exception

In many cases, such errors would occur for an internal reason not because of
an invalid request. So prefer "500 Internal Server Error" over "400 Bad
Request" which might be misleading if the error is actually "internal".

Later on, we should make a proper distinction between true internal errors and
*currently unhandled* client errors. One such case concerns converting
TypeResolverException that might occur when setting a relation to a bad target
into a proper Bad Request (hence the "TODO" in respective test).

cubicweb_jsonschema/api/entities.py

@@ -359,7 +359,7 @@
     detail = str(exc)
     if detail:
         kwargs['detail'] = detail
-    return json_problem(status=400, **kwargs)
+    return json_problem(status=500, **kwargs)
 
 
 def includeme(config):

test/test_api_misc.py

@@ -144,7 +144,8 @@
             cwuser_eid = cnx.find('CWUser', login=u'admin')[0][0]
         self.login()
         url = '/book/%s/author' % book.eid
-        self.webapp.post_json(url, [str(cwuser_eid)], status=400,
+        # TODO: status should be 4xx
+        self.webapp.post_json(url, [str(cwuser_eid)], status=500,
                               headers={'accept': 'application/json'})
 
     def test_put_with_incomplete_data(self):
@@ -345,7 +346,7 @@
         error = ValueError("invalid literal for int() with base 10: 'foo'")
         with patch('cubicweb.req.RequestSessionBase.create_entity',
                    side_effect=error):
-            res = self.webapp.post_json('/cwuser/', data, status=400,
+            res = self.webapp.post_json('/cwuser/', data, status=500,
                                         headers={'Accept': 'application/json'})
             self.assertEqual(res.content_type, 'application/problem+json')
             self.assertEqual(res.json_body, {
@@ -349,8 +350,8 @@
                                         headers={'Accept': 'application/json'})
             self.assertEqual(res.content_type, 'application/problem+json')
             self.assertEqual(res.json_body, {
-                u'status': 400,
-                u'title': u'Bad Request',
+                u'status': 500,
+                u'title': u'Internal Server Error',
                 u'detail': u"invalid literal for int() with base 10: 'foo'",
             })
 
@@ -360,7 +361,7 @@
 
         with patch('cubicweb.req.RequestSessionBase.create_entity',
                    side_effect=NotImplementedError()):
-            res = self.webapp.post_json('/book/', data, status=400,
+            res = self.webapp.post_json('/book/', data, status=500,
                                         headers={'Accept': 'application/json'})
             self.assertEqual(res.content_type, 'application/problem+json')
             self.assertEqual(res.json_body, {
@@ -364,8 +365,8 @@
                                         headers={'Accept': 'application/json'})
             self.assertEqual(res.content_type, 'application/problem+json')
             self.assertEqual(res.json_body, {
-                u'status': 400,
-                u'title': u'Bad Request',
+                u'status': 500,
+                u'title': u'Internal Server Error',
             })