Fix gcu/test_portchannel_interface.py for t2 pr checker (sonic-net#21626)

Summary: Previously, this test case randomly selected DUT out of the testbed. However, if it accidentally select the supervisor as the DUT, it will skip the test case for the whole T2 testbed because the supervisor may not have portchannel config. As an improvement, I used random frontend DUT selection fixture instead. Also, we enable this for T2 PR checker.

Note: this PR performed similar fixes as PR sonic-net#21666. Since PR#21666 got merged first, this PR has been repurposed to just enable the test in VS T2 PR checker.

Signed-off-by: BYGX-wcr <wcr@live.cn>

Author: BYGX-wcr

tests/common/plugins/conditional_mark/tests_mark_conditions_vs_t2.yaml

@@ -305,11 +305,6 @@ generic_config_updater/test_pg_headroom_update.py:
     conditions:
     - asic_type in ['vs'] and 't2' in topo_name
     reason: This test case either cannot pass or should be skipped on virtual chassis
-generic_config_updater/test_portchannel_interface.py:
-  skip:
-    conditions:
-    - asic_type in ['vs'] and 't2' in topo_name
-    reason: This test case either cannot pass or should be skipped on virtual chassis
 generic_config_updater/test_static_route.py:
   skip:
     conditions:

tests/generic_config_updater/test_portchannel_interface.py

@@ -101,7 +101,7 @@ def setup_env(duthosts, enum_rand_one_per_hwsku_frontend_hostname, portchannel_t
     Setup/teardown fixture for portchannel interface config
     Args:
         duthosts: list of DUTs.
-        enum_rand_one_per_hwsku_frontend_hostname: The fixture returns one DUT per hardware SKU
+        enum_rand_one_per_hwsku_frontend_hostname: The fixture returns a randomly selected frontend DuT per HwSKU
     """
     duthost = duthosts[enum_rand_one_per_hwsku_frontend_hostname]
     create_checkpoint(duthost)