object has no attribute '_container' in DockerContainer.__del__(self)

[jankatins]

Describe the bug

AFTER a pipeline run in azure dev ops (which had a failure for the dockerpy + requests/urllib3 incompatibility), I get the following errors:

======================= 14 passed, 131 errors in 24.94s ========================
Exception ignored in: <function DockerContainer.__del__ at 0x7f0d9990da20>
Traceback (most recent call last):
  File "/home/vsts/.cache/pypoetry/virtualenvs/mds-data-core-3AFF4dIC-py3.10/lib/python3.10/site-packages/testcontainers/core/container.py", line 86, in __del__
    if self._container is not None:
AttributeError: 'PostgresContainer' object has no attribute '_container'
Exception ignored in: <function DockerContainer.__del__ at 0x7f0d9990da20>
Traceback (most recent call last):
  File "/home/vsts/.cache/pypoetry/virtualenvs/mds-data-core-3AFF4dIC-py3.10/lib/python3.10/site-packages/testcontainers/core/container.py", line 86, in __del__
    if self._container is not None:
AttributeError: 'ConfluentKafkaContainer' object has no attribute '_container'

ConfluentKafkaContainer is my workaorund for #351

To me this looks like some parts of the class are already gone when the __del__ is called?

The following packages were installed during the run:

testcontainers-kafka = {version = "^0.0.1rc1"}
testcontainers-postgres = {version = "^0.0.1rc1"}
testcontainers-compose = {version = "^0.0.1rc1"}

[jankatins]

The python docs on del() have this:

del() can be executed during interpreter shutdown. As a consequence, the global variables it needs to access (including other modules) may already have been deleted or set to None. Python guarantees that globals whose name begins with a single underscore are deleted from their module before other globals are deleted; if no other references to such globals exist, this may help in assuring that imported modules are still available at the time when the del() method is called.

[tillahoffmann]

This should be resolved once #314 is merged.