Remove usage of "run_until_complete" (#16617)

* De-run_forever()-ization

* Use asyncio.run (or our own implementation on Python <3.7)
* hass.start is only used by tests
* setup_and_run_hass() is now async
* Add "main" async hass.run method
* move SIGINT handling to helpers/signal.py
  * add flag to .run to disable hass's signal handlers
* Teach async_start and async_stop to not step on each other
  (more than necessary)

* shorten over-long lines

* restore missing "import asyncio"

* move run_asyncio to homeassistant.util.async_

* LOGGER: warn => warning

* Add "force" flag to async_stop

only useful for testing

* Add 'attrs==18.2.0' to requirements_all.txt

Required for keeping requirements_test_all.txt in sync, where it is in
turn required to prevent auto-downgrading "attrs" during "pip install"

* Fixes for mypy

* Fix "mock_signal" fixture

* Revert mistaken edit

* Flake8 fixes

* mypy fixes

* pylint fix

* Revert adding attrs== to requirements_test*.txt

solved by using "pip -c"

* Rename "run" to "async_run", as per calling conventions

tests/components/sensor/test_dsmr.py

@@ -182,10 +182,14 @@ def test_reconnect(hass, monkeypatch, mock_connection_factory):
 
     # mock waiting coroutine while connection lasts
     closed = asyncio.Event(loop=hass.loop)
+    # Handshake so that `hass.async_block_till_done()` doesn't cycle forever
+    closed2 = asyncio.Event(loop=hass.loop)
 
     @asyncio.coroutine
     def wait_closed():
         yield from closed.wait()
+        closed2.set()
+        closed.clear()
     protocol.wait_closed = wait_closed
 
     yield from async_setup_component(hass, 'sensor', {'sensor': config})
@@ -195,8 +199,11 @@ def test_reconnect(hass, monkeypatch, mock_connection_factory):
     # indicate disconnect, release wait lock and allow reconnect to happen
     closed.set()
     # wait for lock set to resolve
-    yield from hass.async_block_till_done()
-    # wait for sleep to resolve
+    yield from closed2.wait()
+    closed2.clear()
+    assert not closed.is_set()
+
+    closed.set()
     yield from hass.async_block_till_done()
 
     assert connection_factory.call_count >= 2, \