fix no-unused-prop-types + async class properties and methods

There was an incosistency with access and storage of the usedPropTypes
of a component that would cause proptypes to not be correctly marked as
used if more than one prop was used in the body of an async function
class property or async class method.

Fixes jsx-eslint#1053

---

bug source:

First time around
  - get the parentComponent using utils.getParentComponent() https://github.com/yannickcr/eslint-plugin-react/blob/master/lib/rules/no-unused-prop-types.js#L594
  - save off the usedPropTypes array from what component was found.
  - modify the array with my new used props.
  - set the new array on the node https://github.com/yannickcr/eslint-plugin-react/blob/master/lib/rules/no-unused-prop-types.js#L638
    Note that in this case the node is a MemberExpression
  - Components#set will then just crawl the parents of the current node
  (the MemberExpresion) until one was found in the internal this._list.
  - Because all async FunctionExpressions, ArrowFunctionExpressions, and
  FunctionDeclaration are treated as components of confidence 0 (not a
  component). The unusedPropTypes would be attached
  to this. (Which is usually fine).

However, if the component tries to mark a prop as used again, it will
read from the parentComponent using utils.getParentComponent() (which in
this case will return the class) which does not have the previously used
methods. The array would then be modified (created because it doesnt
exist), and then set them onto the async arrow function overwriting
anything that was previously there.

This change just attaches used props to the found component (where the
previous usedPropTypes are pulled from) if it exists, otherwise to the
current node.

---

Squashed:
Added test cases for factory methods on classes that return async
functions.

Added test cases using the default eslint parser and defining an async
function in the render method.

lib/rules/no-unused-prop-types.js

@@ -635,7 +635,7 @@ module.exports = {
           break;
       }
 
-      components.set(node, {
+      components.set(component ? component.node : node, {
         usedPropTypes: usedPropTypes,
         ignorePropsValidation: ignorePropsValidation
       });