[checkbox-ce-oem] Add check when not able to read node (Bugfix)

[LiaoU3]

Description

It did not handle error correctly when unable to read node. Hence I propose this PR to check check it and make the error message easy to understand.

Unable to read the node

ubuntu@ubuntu:/sys/class/thermal$ sudo cat thermal_zone1/temp
cat: thermal_zone1/temp: Resource temporarily unavailable

ubuntu@ubuntu:/sys/class/thermal$ sudo cat thermal_zone2/temp
cat: thermal_zone2/temp: Resource temporarily unavailable

ubuntu@ubuntu:/sys/class/thermal$ sudo cat thermal_zone3/temp
cat: thermal_zone3/temp: Resource temporarily unavailable

ubuntu@ubuntu:/sys/class/thermal$ sudo cat thermal_zone4/temp
cat: thermal_zone4/temp: Resource temporarily unavailable

Before

Traceback (most recent call last):
  File "/tmp/nest-487v6cqq.1b39665063c258e5aa39344ed03d474aa2913338bf3cafddd02d2ad241fabbf3/thermal_sensor_test.py", line 201, in <module>
    main()
  File "/tmp/nest-487v6cqq.1b39665063c258e5aa39344ed03d474aa2913338bf3cafddd02d2ad241fabbf3/thermal_sensor_test.py", line 197, in main
    args.test_type(args)
  File "/tmp/nest-487v6cqq.1b39665063c258e5aa39344ed03d474aa2913338bf3cafddd02d2ad241fabbf3/thermal_sensor_test.py", line 105, in thermal_monitor_test
    initial_value = thermal_op.temperature
  File "/tmp/nest-487v6cqq.1b39665063c258e5aa39344ed03d474aa2913338bf3cafddd02d2ad241fabbf3/thermal_sensor_test.py", line 69, in temperature
    temp = self._read_node(self.temp_node)
  File "/tmp/nest-487v6cqq.1b39665063c258e5aa39344ed03d474aa2913338bf3cafddd02d2ad241fabbf3/thermal_sensor_test.py", line 55, in _read_node
    return node.read_text().strip("\n")
  File "/snap/checkbox22/current/usr/lib/python3.10/pathlib.py", line 1135, in read_text
    return f.read()
  File "/snap/checkbox22/current/usr/lib/python3.10/codecs.py", line 321, in decode
    data = self.buffer + input
TypeError: can't concat NoneType to bytes

After

2024-07-19 07:24:09 INFO     # Monitor the temperature of thermal_zone1 thermal around 60 seconds
Failed to read node: /sys/class/thermal/thermal_zone1/temp
can't concat NoneType to bytes

Resolved issues

LP#2071402

Documentation

N/A

Tests

https://certification.canonical.com/hardware/202406-34151/submission/381693/

[zongminl]

LGTM, thank you.