Sending empty trailing metadata to a closed stream is ok - it means close this already closed stream

Mirrors a node test, and fix a bug that it found

Needed to properly implement pollset reset

If we already have a status from the wire when we're disconnecting,
leave it in place - don't overwrite it. Fixes disappearing_server_test.

If:
- one thread issues a kick forcing pollset re-evaluation
- concurrently with a second thread forcing a specific poller to be awoken
And:
- both threads kicks are processed as a single wakeup
Then:
- since we enqueue nothing to the exec_ctx in this situation, we responded to the wakeup by doing another poll until the timeout, ignoring urgent work up the stack

Fix this by flagging that a specific worker was designated to be awoken (since this is a good signal that we really really need to wake up), and use that to still re-evaluate the poll set, but with an immediate deadline so that we fall out of the poll loop as soon as possible.

reset option to the mark, create a closed loop config params (empty
message) for consistency with other tests.

For local running one can still tests AllTests, but for C.I. one can
test the 4 of them in parallel (and, importantly, deactivate the remote
interop tests until we fix them on Travis; while keeping the rest).

I had to make the remote tests a subclass of an abstract InteropTests
(like InteropTestsLocalSSL and InteropTestsLocalCleartext), and then
deactivate the abstract InteropTests on the 4 schemes that use it.

Eventually all samples will be tested.

Warnings will be emitted when trying to import through alpha packages.

Still needs implementing format_as_block, and switching input and output
to use sys.stdin.readline() and sys.stdout.write(line).