groupByNode[s]: implement ordering like graphite does

[Dieterbe]

fix #1767

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[Dieterbe]

cc @fqiu7

[replay]

LGTM but wouldn't it make sense to also update the unit tests so they check for the correct order?

[Dieterbe]

i don't like unit tests that are literally the same code as the code that is under test.

[fqiu7]

LGTM. I agree the ordering should be consistent.

[replay]

i don't like unit tests that are literally the same code as the code that is under test.

I agree with that, but that's not how i would implement them. At the moment testGroupByNodes() just sorts the expected and the returned series before comparing. I'd remove that sorting and then make sure that the expected list of metrics is sorted as we expect it to be.

[Dieterbe]

@replay ah yes. we can simply assert that we got them in the same order as how they are specified in the tests, which we can achieve by simply removing the sorting. like this?

[replay]

LGTM