[BUGFIX beta] Use Ember.guidFor to set InternalModel's guid.

[rwjblue]

In future versions of Ember, the Ember.GUID_KEY property may not be the place that guids are stored per object (may be moving to a WeakMap). This change keeps this[GUID_KEY] around for easier debugging (though it isn't required per-se), and uses Ember.guidFor to get the guid and setup the object.

Related to conversation in emberjs/ember.js#14383.

[rwjblue]

/cc @runspired

[rwjblue]

Build will be fixed by #4560.

[runspired]

Only failure in these failures is the thing fixed by #4560

[rwjblue]

I'll rebase now that that is fixed

[rwjblue]

After rebase, I get a super whacky error:

Error: Cannot find module 'source-map/' from '/home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/eslint/node_modules/js-yaml/node_modules/argparse/node_modules/istanbul/node_modules/escodegen/'
    at Function.module.exports [as sync] (/home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/node_modules/resolve/lib/sync.js:33:11)
    at resolvePkg (/home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/resolve-pkg.js:20:18)
    at pkg (/home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/pkg.js:17:20)
    at again (/home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/deps-for.js:18:22)
    at /home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/deps-for.js:27:7
    at Array.forEach (native)
    at again (/home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/deps-for.js:26:55)
    at /home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/deps-for.js:27:7
    at Array.forEach (native)
    at again (/home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/deps-for.js:26:55)
    at /home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/deps-for.js:27:7
    at Array.forEach (native)
    at again (/home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/deps-for.js:26:55)
    at /home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/deps-for.js:27:7
    at Array.forEach (native)
    at again (/home/travis/build/emberjs/data/node_modules/ember-cli-eslint/node_modules/broccoli-lint-eslint/node_modules/broccoli-persistent-filter/node_modules/hash-for-dep/lib/deps-for.js:26:55)

[rwjblue]

Finally passing (for Travis builds).

[bmac]

Thanks @rwjblue.