Add test for MMR::on_initialize() vs Session::on_initialize()

[bkontur]

Based on element discussion.

[acatangiu]

@bkontur I can't see the "element discussion" anymore - do you still have the details of this issue?

[serban300]

I think it was related to checking that MMR::on_initialize() is called before Session::on_initialize(). We weren't sure this would still be the case after construct runtime v2. But in the meanwhile I think we rolled-back the logic related to calling MMR::on_initialize() before Session::on_initialize() ? So maybe we can close this issue.

[acatangiu]

hmm, in that case we could still have the test, but checking the order:

1. Session
2. MMR