Upgrade ember-source for MU new blueprints

[ppcano]

Closes #8316

The blueprint should point to the most recent canary tarball (via ember-source-channel-url). We need to use canary specifically because MU requires a feature flag to be enabled which is only possible in canary builds.

The last upgrade was done by #7976

[rwjblue]

This looks good, thank you!

Perhaps in a follow up PR, we could tweak the blueprint to actually fetch the latest each time. What do you think?

[ppcano]

I thought about that too when reviewing https://github.com/ember-cli/ember-octane-blueprint/blob/master/index.js, but this change will likely require to change some ember-cli tests.

As you see in the PR the test fixtures are also changed because the content of the npm/yarn file is compared and validated.

I am not sure atm how to change the tests if the ember-sourcevalue is dynamically fetched.

We follow the same approach when upgrading the ember-source of the Classic app as show at a824605

[rwjblue]

I am not sure atm how to change the tests if the ember-sourcevalue is dynamically fetched.

If you take a look here, we already do a custom matcher for package.json so taht we can account for dynamic ember-cli versions, I think this function can fairly easily be extended to support custom ember-source version. What do you think?

ember-cli/tests/acceptance/new-test.js

Line 428 in 413b260

function checkPackageJson(fixtureName) {