fix(usbrelay): poll for status to confirm

The usbrelay command is async, hence we cannot immediately after
changing the state check if it became active. Instead, we need to poll
for some time and report back either if the state changed, or on
timeout. To leave sufficent time for other parts of the code, we check
until half of the RPC timeout is expired.

Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>

mtda/power/usbrelay.py

@@ -12,10 +12,12 @@
 # System imports
 import os
 import re
+import time
 import subprocess
 
 # Local imports
 from mtda.power.controller import PowerController
+import mtda.constants as CONSTS
 
 
 class UsbRelayPowerController(PowerController):
@@ -49,12 +51,12 @@ def command(self, args):
     def on(self):
         if self._set_lines("1") is False:
             return False
-        return self.status() == self.POWER_ON
+        return self._poll_status_until(self.POWER_ON)
 
     def off(self):
         if self._set_lines("0") is False:
             return False
-        return self.status() == self.POWER_OFF
+        return self._poll_status_until(self.POWER_OFF)
 
     def status(self):
         statuses = self._get_lines()
@@ -75,6 +77,13 @@ def status(self):
                 result = self.POWER_UNSURE
         return result
 
+    def _poll_status_until(self, desired_state):
+        for i in range(0, CONSTS.RPC.TIMEOUT // 2 + 1):
+            if self.status() == desired_state:
+                return True
+            time.sleep(0.5)
+        return False
+
     def _get_lines(self):
         result = {}
         try: