power_Standby: Don't check AC if force_discharge

BUG=b:144726667
TEST=power_Dashboard.fast_lab

Change-Id: I52a0e4cd6db2bff0454cc656dcc99d8263a3de0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/1968048
Tested-by: Puthikorn Voravootivat <puthik@chromium.org>
Commit-Queue: Puthikorn Voravootivat <puthik@chromium.org>
Auto-Submit: Puthikorn Voravootivat <puthik@chromium.org>
Reviewed-by: Mengqi Guo <mqg@chromium.org>
diff --git a/client/site_tests/power_Standby/power_Standby.py b/client/site_tests/power_Standby/power_Standby.py
index 6155aee..1d17405 100644
--- a/client/site_tests/power_Standby/power_Standby.py
+++ b/client/site_tests/power_Standby/power_Standby.py
@@ -46,7 +46,7 @@
 
         power_stats = power_status.get_status()
 
-        if not ac_ok and power_stats.on_ac():
+        if not force_discharge and not ac_ok and power_stats.on_ac():
             raise error.TestError('On AC, please unplug power supply.')
 
         if force_discharge: