[Port to 2.3-develop] Sort configurable attribute options by sort_order

[wardcapp]

Port of PR #12963 to the 2.3-develop branch.
See github issue #7441, internal ticket MAGETWO-61484 and PR #12420.

Description

Resolves the issue documented in GitHub ticket #7441. A similar PR was opened before (#12963), which is now ported to the 2.3-develop branch.

Fixed Issues

1. Configurable attribute options are not sorted #7441: Configurable attribute options are not sorted

Manual testing scenarios

(copied over from PR #12420, which is still valid)
Steps to reproduce
Create a configurable attribute and add two options at least.
Create a configurable product for these options.
Go to the product page and see the configurable attribute select (options).
Change attribute options sort order and flush all caches.
Go to the product page and see the configurable attribute select (options) looks like before.

Expected result:
Configurable options HAVE been reordered.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests
• All automated tests passed successfully (was tested with success locally, awaiting results from Travis)

[wardcapp]

The jasmine test failures (reported by Travis) do not seem to relate to the changes made and I cannot reproduce the failures locally (using the Luma theme, blank was tested as well):

...
Magento_Ui/js/form/components/collection
   "initElement" method
     ✓ Check for defined 
     ✓ Check answer type
     ✓ Check returned value if method called with object arguments
     ✓ Check returned value type if method called object arguments
     ✓ Check call method "this.bubble" inner initElement method
   "initChildren" method
     ✓ Check for defined 
     ✓ Check answer type
     ✓ Check returned value if method called without arguments
     ✓ Check returned value type if method called without arguments
     ✓ Check call method "this.source.get" inner initElement method
     ✓ Check this.initialItems property affter called initChildren
   "addChild" method
     ✓ Check for defined 
     ✓ Check answer type
     ✓ Check returned value if method called with arguments
     ✓ Check returned value type if method called with arguments
     ✓ Check this.childIndex property affter called addChild
   "hasChanged" method
     ✓ Check for defined 
     ✓ Check answer type
     ✓ Check returned value if method called without arguments
     ✓ Check returned value type if method called without arguments
   "validate" method
     ✓ Check for defined 
     ✓ Check answer type
     ✓ Check returned value if method called without arguments
     ✓ Check returned value type if method called without arguments
   "removeAddress" method
     ✓ Check for defined 
     ✓ Check answer type
...
log: Deprecation warning: value provided is not in a recognized ISO format. moment construction falls back to js Date(), which is not reliable across all browsers and versions. Non ISO date formats are discouraged and will be removed in an upcoming major release. Please refer to http://momentjs.com/guides/#/warnings/js-date/ for more info.
Arguments: 
[0] _isAMomentObject: true, _isUTC: false, _useUTC: false, _l: undefined, _i: 01/5/2018, _f: undefined, _strict: undefined, _locale: [object Object]
undefined
   ✓ writes picked date's value to assigned observable
 i18n binding
   ✓ if inline translation is off, just set text for element
   ✓ if inline translation is on, and there is no translation for this text, set original text for element
 Magento_Ui/js/form/form
   "initAdapter" method
     ✓ Check for defined 
     ✓ Check method type
     ✓ Check returned value if method called without arguments
     ✓ Check returned value type if method called without arguments
   "initialize" method
     ✓ Check for defined 
     ✓ Check method type
     ✓ Check returned value if method called without arguments
     ✓ Check returned value type if method called without arguments
   "initConfig" method
     ✓ Check for defined 
     ✓ Check method type
     ✓ Check returned value if method called without arguments
     ✓ Check returned value type if method called without arguments
     ✓ Check this.selector property (is modify in initConfig method)
   "hideLoader" method
     ✓ Check for defined 
     ✓ Check method type
     ✓ Check returned value if method called without arguments
     ✓ Check returned value type if method called without arguments
   "save" method
     ✓ Check for defined 
     ✓ Check method type
   "submit" method
     ✓ Check for defined 
     ✓ Check method type
   "validate" method
     ✓ Check for defined 
     ✓ Check method type
   "reset" method
     ✓ Check for defined 
     ✓ Check method type
...

885 specs in 106.057s.
>> 0 failures
(node:3082) DeprecationWarning: Calling an asynchronous function without callback is deprecated.

Done.


Execution Time (2018-01-05 22:09:54 UTC-0)
jasmine:luma    1m 50.5s  ▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇▇ 99%
Total 1m 51.4s

885 specs in 104.042s.
>> 0 failures
(node:3127) DeprecationWarning: Calling an asynchronous function without callback is deprecated.

Done.

Not quite sure what went wrong when Travis executed those tests. A newer PR, #13012, strangely did pass the same tests.