Fix for problem that files like bonding_masters are not skipped

[schmidax]

General information

This pull request fixes the problem that the script lnx_container_host_if.linux does not ignore possible files like bonding_masters as expected but generates empty values that are sent to the check_mk server which causes the plugin to crash:

Error message:
ValueError (not enough values to unpack (expected 2, got 1))

Traceback:

File "/omd/sites/nms_k8s/lib/python3/cmk/base/agent_based/data_provider.py", line 106, in _parse_raw_data
    return parse_function(list(raw_data))
  File "/omd/sites/nms_k8s/lib/python3/cmk/base/plugins/agent_based/section_lnx_container_host_if.py", line 138, in parse_lnx_container_host_if
    return [_create_interface(_parse_raw_stats(i)) for i in string_table], {}
  File "/omd/sites/nms_k8s/lib/python3/cmk/base/plugins/agent_based/section_lnx_container_host_if.py", line 138, in <listcomp>
    return [_create_interface(_parse_raw_stats(i)) for i in string_table], {}
  File "/omd/sites/nms_k8s/lib/python3/cmk/base/plugins/agent_based/section_lnx_container_host_if.py", line 47, in _parse_raw_stats
    k, v = stats.split("\v")

Bug reports

Read following Post:
Network monitoring using Kubernetes Agent fails due to network bonding

Proposed changes

Now the bash script checks first whether the path is a folder or a file and then checks whether the folder is empty or not.