fix 'eb --show-system-info' on Apple M1 system

[boegel]

This fixes various small issues that pop up on Apple M1:

• add fallback to "sysctl -n machdep.cpu.brand_string" in get_cpu_vendor to determine CPU type, since "sysctl -n machdep.cpu.vendor" is not supported on Apple M1 systems;
• add Apple as known CPU vendor;
• avoid that get_cpu_speed crashes when it fails to determine CPU speed via "sysctl -n hw.cpufrequency_max" (which returns empty string on Apple M1), and just return None;
• avoid crash in get_cpu_features because "sysctl -n machdep.cpu.extfeatures" is not supported on Apple M1 (and leave list of CPU features empty, for now);
• also includes fixes for systemtools tests so they pass on Apple M1;

Also requires #4014 for all systemtools tests to pass on Apple M1

fixes #4013

[ocaisa]

This also looks ok, can you add an example of the output since I can't test this?

[boegel]

This fixes a hard crash early on when running eb on Apple M1:

Traceback (most recent call last):
  File "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/python3.8/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/Users/kehoste/work/easybuild-framework/easybuild/main.py", line 597, in <module>
    main()
  File "/Users/kehoste/work/easybuild-framework/easybuild/main.py", line 234, in main
    init_session_state = session_state()
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/testing.py", line 137, in session_state
    'system_info': get_system_info(),
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/systemtools.py", line 1068, in get_system_info
    'cpu_speed': get_cpu_speed(),
  File "/Users/kehoste/work/easybuild-framework/easybuild/tools/systemtools.py", line 538, in get_cpu_speed
    cpu_freq = float(out.strip()) // (1000 ** 2)
ValueError: could not convert string to float: ''

[boegel]

Example output on Apple M1:

$ eb --show-system-info
System information (vpne020.ugent.be):

* OS:
  -> name: UNKNOWN
  -> type: Darwin
  -> version: UNKNOWN
  -> platform name: arm64-apple-darwin

* CPU:
  -> vendor: Apple
  -> architecture: AArch64
  -> family: ARM
  -> arch name: m1
  -> model: Apple M1
  -> speed: None
  -> cores: 8
  -> features:

* software:
  -> glibc version: UNKNOWN
  -> Python binary: /Library/Developer/CommandLineTools/usr/bin/python3
  -> Python version: 3.8.9

There's room for improvement, but this is way better than only producing a nasty traceback on macOS @ Apple M1...

[ocaisa]

Agreed