Find nni lib from the following locations in order
    Return nni root directory if it exists

def get_nni_installation_path():
    ''' Find nni lib from the following locations in order
    Return nni root directory if it exists
    '''
    def try_installation_path_sequentially(*sitepackages):
        '''Try different installation path sequentially util nni is found.
        Return None if nothing is found
        '''
        def _generate_installation_path(sitepackages_path):
            python_dir = get_python_dir(sitepackages_path)
            entry_file = os.path.join(python_dir, 'nni', 'main.js')
            if os.path.isfile(entry_file):
                return python_dir
            return None

        for sitepackage in sitepackages:
            python_dir = _generate_installation_path(sitepackage)
            if python_dir:
                return python_dir
        return None

    if os.getenv('VIRTUAL_ENV'):
        # if 'virtualenv' package is used, `site` has not attr getsitepackages, so we will instead use VIRTUAL_ENV
        # Note that conda venv will not have VIRTUAL_ENV
        python_dir = os.getenv('VIRTUAL_ENV')
    else:
        python_sitepackage = site.getsitepackages()[0]
        # If system-wide python is used, we will give priority to using `local sitepackage`--"usersitepackages()" given that nni exists there
        if python_sitepackage.startswith('/usr') or python_sitepackage.startswith('/Library'):
            python_dir = try_installation_path_sequentially(site.getusersitepackages(), site.getsitepackages()[0])
        else:
            python_dir = try_installation_path_sequentially(site.getsitepackages()[0], site.getusersitepackages())

    if python_dir:
        entry_file = os.path.join(python_dir, 'nni', 'main.js')
        if os.path.isfile(entry_file):
            return os.path.join(python_dir, 'nni')
    print_error('Fail to find nni under python library')
    exit(1)