PROTON-2748: Raw connection async close fix and tests.

[cliffjansen]

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[astitcher]

@cliffjansen I really like how this has turned out now. Are you finished or are there more changes due to adding new tests?

[cliffjansen]

I will check in the changes so far to get some extended CI going.

Todo: additional tests as suggested and rename the test. I will leave the pull and JIRA open until they are done and will incorporate additional suggestions.

I propose changing raw_wake_test to raw_connection_proactor_test to reflect it tests the functionality of the proactor implementation of raw connections whereas the existing raw_connection_test tests the proactor-independent bits of the internal/external API without a running proactor.

[astitcher]

The new commits lgtm