Mock path early so it will applied to sonic_py_common, mock platform_chassis (sonic-net#188)

#### Description
Following sonic-net/sonic-platform-daemons#187 to fix the same issue with other packages

#### Motivation and Context
This is blocking sonic-net#7655

#### How Has This Been Tested?
Unit test

Author: qiluo-msft

sonic-psud/tests/mocked_libs/swsscommon/swsscommon.py

@@ -2,6 +2,8 @@
     Mock implementation of swsscommon package for unit testing
 '''
 
+from swsssdk import ConfigDBConnector, SonicDBConfig, SonicV2Connector
+
 STATE_DB = ''
 
 

sonic-psud/tests/test_DaemonPsud.py

@@ -10,21 +10,22 @@
     from unittest import mock
 else:
     import mock
-from sonic_py_common import daemon_base
 
 from .mock_platform import MockChassis, MockFan, MockPsu
 
 SYSLOG_IDENTIFIER = 'psud_test'
 NOT_AVAILABLE = 'N/A'
 
-daemon_base.db_connect = mock.MagicMock()
 
 tests_path = os.path.dirname(os.path.abspath(__file__))
 
 # Add mocked_libs path so that the file under test can load mocked modules from there
 mocked_libs_path = os.path.join(tests_path, "mocked_libs")
 sys.path.insert(0, mocked_libs_path)
 
+from sonic_py_common import daemon_base
+daemon_base.db_connect = mock.MagicMock()
+
 # Add path to the file under test so that we can load it
 modules_path = os.path.dirname(tests_path)
 scripts_path = os.path.join(modules_path, "scripts")

sonic-psud/tests/test_psud.py

@@ -11,7 +11,7 @@
     import mock
 from sonic_py_common import daemon_base
 
-from .mock_platform import MockPsu
+from .mock_platform import MockPsu, MockChassis
 
 tests_path = os.path.dirname(os.path.abspath(__file__))
 
@@ -179,6 +179,7 @@ def test_log_on_status_changed():
     mock_logger.log_warning.assert_called_with(abnormal_log)
 
 
+@mock.patch('psud.platform_chassis', mock.MagicMock())
 @mock.patch('psud.DaemonPsud.run')
 def test_main(mock_run):
     mock_run.return_value = False

sonic-syseepromd/tests/mocked_libs/swsscommon/swsscommon.py

@@ -2,6 +2,8 @@
     Mock implementation of swsscommon package for unit testing
 '''
 
+from swsssdk import ConfigDBConnector, SonicDBConfig, SonicV2Connector
+
 STATE_DB = ''
 
 
@@ -23,6 +25,9 @@ def get(self, key):
             return self.mock_dict[key]
         return None
 
+    def get_size(self):
+        return (len(self.mock_dict))
+
 
 class FieldValuePairs:
     fv_dict = {}

sonic-syseepromd/tests/test_syseepromd.py

@@ -9,19 +9,19 @@
     from unittest import mock
 else:
     import mock
-from sonic_py_common import daemon_base
 
 SYSLOG_IDENTIFIER = 'syseepromd_test'
 NOT_AVAILABLE = 'N/A'
 
-daemon_base.db_connect = mock.MagicMock()
-
 tests_path = os.path.dirname(os.path.abspath(__file__))
 
 # Add mocked_libs path so that the file under test can load mocked modules from there
 mocked_libs_path = os.path.join(tests_path, 'mocked_libs')
 sys.path.insert(0, mocked_libs_path)
 
+from sonic_py_common import daemon_base
+daemon_base.db_connect = mock.MagicMock()
+
 # Add path to the file under test so that we can load it
 modules_path = os.path.dirname(tests_path)
 scripts_path = os.path.join(modules_path, 'scripts')