Homekit: Bugfix Thermostat Fahrenheit support (#13477)

* Bugfix thermostat temperature conversion
* util -> temperature_to_homekit
* util -> temperature_to_states
* util -> convert_to_float
* Added tests, deleted log msg

homeassistant/components/homekit/util.py

@@ -5,8 +5,9 @@ import voluptuous as vol
 
 from homeassistant.core import split_entity_id
 from homeassistant.const import (
-    ATTR_CODE)
+    ATTR_CODE, TEMP_CELSIUS)
 import homeassistant.helpers.config_validation as cv
+import homeassistant.util.temperature as temp_util
 from .const import HOMEKIT_NOTIFY_ID
 
 _LOGGER = logging.getLogger(__name__)
@@ -44,3 +45,21 @@ def show_setup_message(bridge, hass):
 def dismiss_setup_message(hass):
     """Dismiss persistent notification and remove QR code."""
     hass.components.persistent_notification.dismiss(HOMEKIT_NOTIFY_ID)
+
+
+def convert_to_float(state):
+    """Return float of state, catch errors."""
+    try:
+        return float(state)
+    except (ValueError, TypeError):
+        return None
+
+
+def temperature_to_homekit(temperature, unit):
+    """Convert temperature to Celsius for HomeKit."""
+    return round(temp_util.convert(temperature, unit, TEMP_CELSIUS), 1)
+
+
+def temperature_to_states(temperature, unit):
+    """Convert temperature back from Celsius to Home Assistant unit."""
+    return round(temp_util.convert(temperature, TEMP_CELSIUS, unit), 1)