Map Alexa StepVolume responses to volume_up/down (#12467)

It turns out I misunderstood which media_player services are available
when a media player supports StepVolume. This PR maps the Alexa
StepSpeaker messages to the volume_up and volume_down services.

Currently Alexa allows you to specify the number of steps but the media
player volume_up and volume_down services don't support this. For now I
just look to see if the steps are +/- and call up/down accordingly.

homeassistant/components/alexa/smart_home.py

@@ -1178,20 +1178,24 @@ def async_api_adjust_volume(hass, config, request, entity):
 @asyncio.coroutine
 def async_api_adjust_volume_step(hass, config, request, entity):
     """Process an adjust volume step request."""
-    volume_step = round(float(request[API_PAYLOAD]['volumeSteps'] / 100), 2)
-
-    current_level = entity.attributes.get(media_player.ATTR_MEDIA_VOLUME_LEVEL)
-
-    volume = current_level + volume_step
+    # media_player volume up/down service does not support specifying steps
+    # each component handles it differently e.g. via config.
+    # For now we use the volumeSteps returned to figure out if we
+    # should step up/down
+    volume_step = request[API_PAYLOAD]['volumeSteps']
 
     data = {
         ATTR_ENTITY_ID: entity.entity_id,
-        media_player.ATTR_MEDIA_VOLUME_LEVEL: volume,
     }
 
-    yield from hass.services.async_call(
-        entity.domain, media_player.SERVICE_VOLUME_SET,
-        data, blocking=False)
+    if volume_step > 0:
+        yield from hass.services.async_call(
+            entity.domain, media_player.SERVICE_VOLUME_UP,
+            data, blocking=False)
+    elif volume_step < 0:
+        yield from hass.services.async_call(
+            entity.domain, media_player.SERVICE_VOLUME_DOWN,
+            data, blocking=False)
 
     return api_message(request)