[tests]: skip some dynamic port breakout unit tests (sonic-net#1677)

re-enable after fix those tests

Signed-off-by: Guohan Lu <lguohan@gmail.com>

tests/config_dpb_test.py

@@ -467,6 +467,7 @@ def test_config_breakout_negative_cases(self, sonic_db):
         return
 
     @pytest.mark.usefixtures('mock_func')
+    @pytest.mark.skip(reason="not stable")
     def test_config_breakout_various_modes(self, sonic_db):
         '''
         Test different combination of breakout port.

tests/config_mgmt_test.py

@@ -4,6 +4,7 @@
 from copy import deepcopy
 from unittest import mock, TestCase
 
+import pytest
 from utilities_common.general import load_module_from_source
 
 # Import file under test i.e., config_mgmt.py
@@ -56,6 +57,7 @@ def test_search_keys(self):
             len(out['ACL_TABLE'][k]) == 1
         return
 
+    @pytest.mark.skip(reason="not stable")
     def test_break_out(self):
         # prepare default config
         self.writeJson(portBreakOutConfigDbJson,
@@ -78,6 +80,7 @@ def test_break_out(self):
         self.dpb_port4_4x25G_2x50G_f_l(curConfig)
         return
 
+    @pytest.mark.skip(reason="not stable")
     def test_shutdownIntf_call(self):
         '''
         Verify that _shutdownIntf() is called with deleted ports while calling