[Python] Reset chip error in test commissioner (project-chip#34001)

* [Python] Reset chip error in test commissioner

Make sure to reset the chip error in test commissioner on reset. This
avoid spurious errors. The Python side reads the error as soon as
mTestCommissionerUsed is set, which happens unconditionally. Hence
clearing the error is necessary.

* [Python] Remove unexpected exception in TC_CGEN_2_4.py

With the test commissioner properly resetting the error code the
spurious exception is no longer thrown. Remove the exception handling
from the test.

Author: agners

src/controller/python/OpCredsBinding.cpp

@@ -259,6 +259,7 @@ class TestCommissioner : public chip::Controller::AutoCommissioner
         mPrematureCompleteAfter = chip::Controller::CommissioningStage::kError;
         mReadCommissioningInfo  = chip::Controller::ReadCommissioningInfo();
         mNeedsDST               = false;
+        mCompletionError        = CHIP_NO_ERROR;
     }
     bool GetTestCommissionerUsed() { return mTestCommissionerUsed; }
     void OnCommissioningSuccess(chip::PeerId peerId) { mReceivedCommissioningSuccess = true; }

src/python_testing/TC_CGEN_2_4.py

@@ -104,12 +104,9 @@ async def test_TC_CGEN_2_4(self):
         logging.info('Step 16 - TH2 fully commissions the DUT')
         self.th2.ResetTestCommissioner()
 
-        ctx = asserts.assert_raises(ChipStackError)
-        with ctx:
-            self.th2.CommissionOnNetwork(
-                nodeId=self.dut_node_id, setupPinCode=params.setupPinCode,
-                filterType=ChipDeviceCtrl.DiscoveryFilterType.LONG_DISCRIMINATOR, filter=self.discriminator)
-        asserts.assert_true(ctx.exception.chip_error.sdk_code == 0x02, 'Unexpected error code returned from CommissioningComplete')
+        self.th2.CommissionOnNetwork(
+            nodeId=self.dut_node_id, setupPinCode=params.setupPinCode,
+            filterType=ChipDeviceCtrl.DiscoveryFilterType.LONG_DISCRIMINATOR, filter=self.discriminator)
         logging.info('Commissioning complete done.')
 
         logging.info('Step 17 - TH1 sends an arm failsafe')