Fix low-hanging rubocop gripes (#8458)

* rubocop: quit being so picky

* rubocop: miscellany

* rubocop: prefer present to blank

.rubocop.yml

@@ -62,6 +62,9 @@ Metrics/ParameterLists:
 Metrics/PerceivedComplexity:
   Max: 20
 
+Naming/MemoizedInstanceVariableName:
+  Enabled: false
+
 Rails:
   Enabled: true
 
@@ -71,6 +74,9 @@ Rails/HasAndBelongsToMany:
 Rails/SkipsModelValidations:
   Enabled: false
 
+Rails/HttpStatus:
+  Enabled: false
+
 Style/ClassAndModuleChildren:
   Enabled: false