[consutil] Fix consule CLI and enhance unittest (sonic-net#3360)

**What I did?**
1. Bugfix for console CLI (This is introduced by [consutil] replace shell=True sonic-net#2725, * cannot be treated as wildcard correctly).
```
admin@sonic:~$ show line
ls: cannot access '/dev/C0-*': No such file or directory
```
2. Enhance UT to avoid regression mentioned in 1.
3. Fix incorrect statement in UT.
4. Fix critical Flake8 error.

**How to verify it**
1. Verified on Nokia-7215 MC0 device.
2. Verified by UT

Sign-Off By: Zhijian Li <zhijianli@microsoft.com>

Author: lizhijianrd

consutil/lib.py

@@ -277,7 +277,7 @@ def init_device_prefix():
     @staticmethod
     def list_console_ttys():
         """Lists all console tty devices"""
-        cmd = ["ls", SysInfoProvider.DEVICE_PREFIX + "*"]
+        cmd = ["bash", "-c", "ls " + SysInfoProvider.DEVICE_PREFIX + "*"]
         output, _ = SysInfoProvider.run_command(cmd, abort=False)
         ttys = output.split('\n')
         ttys = list([dev for dev in ttys if re.match(SysInfoProvider.DEVICE_PREFIX + r"\d+", dev) != None])

tests/console_mock/dev/ttyACM1

@@ -14,10 +14,15 @@
 
 from click.testing import CliRunner
 from utilities_common.db import Db
-from consutil.lib import *
+from consutil.lib import ConsolePortProvider, ConsolePortInfo, ConsoleSession, SysInfoProvider, DbUtils, \
+    InvalidConfigurationError, LineBusyError, LineNotFoundError, ConnectionFailedError
 from sonic_py_common import device_info
 from jsonpatch import JsonPatchConflict
 
+SCRIPT_DIR = os.path.dirname(os.path.realpath(__file__))
+CONSOLE_MOCK_DIR = SCRIPT_DIR + "/console_mock"
+
+
 class TestConfigConsoleCommands(object):
     @classmethod
     def setup_class(cls):
@@ -543,17 +548,15 @@ def test_sys_info_provider_init_device_prefix_plugin(self):
         with mock.patch("builtins.open", mock.mock_open(read_data="C0-")):
             SysInfoProvider.init_device_prefix()
             assert SysInfoProvider.DEVICE_PREFIX == "/dev/C0-"
-            SysInfoProvider.DEVICE_PREFIX = "/dev/ttyUSB"
 
-    @mock.patch('consutil.lib.SysInfoProvider.run_command', mock.MagicMock(return_value=("/dev/ttyUSB0\n/dev/ttyACM1", "")))
     def test_sys_info_provider_list_console_ttys(self):
-        SysInfoProvider.DEVICE_PREFIX == "/dev/ttyUSB"
+        SysInfoProvider.DEVICE_PREFIX = CONSOLE_MOCK_DIR + "/dev/ttyUSB"
         ttys = SysInfoProvider.list_console_ttys()
         print(SysInfoProvider.DEVICE_PREFIX)
         assert len(ttys) == 1
 
-    @mock.patch('consutil.lib.SysInfoProvider.run_command', mock.MagicMock(return_value=("", "ls: cannot access '/dev/ttyUSB*': No such file or directory")))
     def test_sys_info_provider_list_console_ttys_device_not_exists(self):
+        SysInfoProvider.DEVICE_PREFIX = CONSOLE_MOCK_DIR + "/dev_not_exist/ttyUSB"
         ttys = SysInfoProvider.list_console_ttys()
         assert len(ttys) == 0
 
@@ -563,7 +566,7 @@ def test_sys_info_provider_list_console_ttys_device_not_exists(self):
         """
     @mock.patch('consutil.lib.SysInfoProvider.run_command', mock.MagicMock(return_value=all_active_processes_output))
     def test_sys_info_provider_list_active_console_processes(self):
-        SysInfoProvider.DEVICE_PREFIX == "/dev/ttyUSB"
+        SysInfoProvider.DEVICE_PREFIX = "/dev/ttyUSB"
         procs = SysInfoProvider.list_active_console_processes()
         assert len(procs) == 1
         assert "0" in procs
@@ -572,15 +575,15 @@ def test_sys_info_provider_list_active_console_processes(self):
     active_process_output = "13751 Wed Mar  6 08:31:35 2019 /usr/bin/sudo picocom -b 9600 -f n /dev/ttyUSB1"
     @mock.patch('consutil.lib.SysInfoProvider.run_command', mock.MagicMock(return_value=active_process_output))
     def test_sys_info_provider_get_active_console_process_info_exists(self):
-        SysInfoProvider.DEVICE_PREFIX == "/dev/ttyUSB"
+        SysInfoProvider.DEVICE_PREFIX = "/dev/ttyUSB"
         proc = SysInfoProvider.get_active_console_process_info("13751")
         assert proc is not None
         assert proc == ("1", "13751",  "Wed Mar  6 08:31:35 2019")
 
     active_process_empty_output = ""
     @mock.patch('consutil.lib.SysInfoProvider.run_command', mock.MagicMock(return_value=active_process_empty_output))
     def test_sys_info_provider_get_active_console_process_info_nonexists(self):
-        SysInfoProvider.DEVICE_PREFIX == "/dev/ttyUSB"
+        SysInfoProvider.DEVICE_PREFIX = "/dev/ttyUSB"
         proc = SysInfoProvider.get_active_console_process_info("2")
         assert proc is None