read_excel tests sporadically fail in CI because some file handles remain open

[vnlitvinov]

System information

• OS Platform and Distribution (e.g., Linux Ubuntu 16.04): Linux
• Modin version (modin.__version__): master (e.g. 3e62906)
• Python version: any
• Code we can use to reproduce: watch for read_io tests

Describe the problem

Something seems to be reading statistics from time to time, as tests that fail are always having files from /proc/<pid>/<something> left open.

Source code / logs

Example: https://github.com/modin-project/modin/runs/1572578393#step:22:64

_____________________ TestExcel.test_read_excel_index_col ______________________

a = (<modin.pandas.test.test_io.TestExcel object at 0x7f0df11ea9d0>,), kw = {}
fstart = [], leaks = [('/proc/10921/stat', 60)], item = ('/proc/10921/stat', 60)

    @functools.wraps(func)
    def check(*a, **kw):
        fstart = _get_open_files()
        try:
            return func(*a, **kw)
        finally:
            leaks = []
            for item in _get_open_files():
                try:
                    fstart.remove(item)
                except ValueError:
                    leaks.append(item)
            assert (
                not leaks
>           ), f"Unexpected open handles left for: {', '.join(item[0] for item in leaks)}"
E           AssertionError: Unexpected open handles left for: /proc/10921/stat

More info: the check was introduced in #2514