Avoid using `len(x)` to check if x is empty

This cases are using `len()` to check if collection has items.
As collections have a boolean representation too, directly check
for true / false.

Change-Id: I1e552db99fbe6d33ad43bb710af924261dcebb46

keystone/common/validation/validators.py

@@ -43,7 +43,7 @@ class SchemaValidator(object):
         except jsonschema.ValidationError as ex:
             # NOTE: For whole OpenStack message consistency, this error
             # message has been written in a format consistent with WSME.
-            if len(ex.path) > 0:
+            if ex.path:
                 # NOTE(lbragstad): Here we could think about using iter_errors
                 # as a method of providing invalid parameters back to the
                 # user.

keystone/oauth1/controllers.py

@@ -303,7 +303,7 @@ class OAuthControllerV3(controller.V3Controller):
             body=context['query_string'],
             headers=headers)
         params = oauth1.extract_non_oauth_params(b)
-        if len(params) != 0:
+        if params:
             msg = _('There should not be any non-oauth parameters')
             raise exception.Unauthorized(message=msg)
 

keystone/tests/hacking/checks.py

@@ -305,7 +305,7 @@ class CheckForLoggingIssues(BaseASTChecker):
                 return super(CheckForLoggingIssues, self).generic_visit(node)
 
             # the call must have arguments
-            if not len(node.args):
+            if not node.args:
                 return super(CheckForLoggingIssues, self).generic_visit(node)
 
             if method_name == 'debug':