vt_init raises errors when importing avocado-vt modules into python session

[smitterl]

With the latest master today (avocado 94.0) there are errors when loading avocado-vt modules into python3 session.
I tried using avocado 92lts and 82lts but this issue reproduces.
After the error message, the module is available and I confirmed the log_line function that can't be imported is available in the utils_misc. I'm not familiar with the importlib, any idea how to debug this?

$ python3 --version
Python 3.6.8
$ cd avocado
$ pip install -r requirements-dev.txt
$ pip install -e .
$ cd ../avocado-vt
$ pip install -r 
$ pip install -r requirements.txt
$ pip install -e .
$ python3
>> from virttest import utils_misc
No python imaging library installed. Screendump and Windows guest BSOD detection are disabled. In order to enable it, please install python-imaging or the equivalent for your distro.
No python imaging library installed. PPM image conversion to JPEG disabled. In order to enable it, please install python-imaging or the equivalent for your distro.

Reproduced traceback from: /home/smitterl/NotBackedUp/avocado-tmp/avocado/avocado/core/extension_manager.py:216
Traceback (most recent call last):
  File "/home/smitterl/NotBackedUp/avocado-tmp/avocado-vt/avocado_vt/plugins/vt_init.py", line 276, in initialize
    virt_loader = getattr(importlib.import_module('avocado_vt.loader'),
  File "/usr/lib64/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/smitterl/NotBackedUp/avocado-tmp/avocado-vt/avocado_vt/loader.py", line 33, in <module>
    from .test import VirtTest
  File "/home/smitterl/NotBackedUp/avocado-tmp/avocado-vt/avocado_vt/test.py", line 33, in <module>
    from virttest import utils_env
  File "/home/smitterl/NotBackedUp/avocado-tmp/avocado-vt/virttest/utils_env.py", line 19, in <module>
    from virttest import ip_sniffing
  File "/home/smitterl/NotBackedUp/avocado-tmp/avocado-vt/virttest/ip_sniffing.py", line 21, in <module>
    from virttest.utils_misc import log_line
ImportError: cannot import name 'log_line'

Error running method "initialize" of plugin "vt-init": cannot import name 'log_line'
>>>

[chunfuwen]

virttest/utils_logfile.py and virttest/utils_misc.py duplicate the same code : def log_line(filename, line) implementation. I try import log_line from virttest/utils_logfile.py in the file virttest/ip_sniffing.py, the issue can be fixed

[chunfuwen]

#3392