Fix ALPEH-517 confidential clean up

[olethanh]

ConfidentialQemuVM teardown was trying to close the journal stdout but they were not properly set. (they are set properly in qemuvm)

python3[1738237]: 2025-04-14 13:41:13,531 | ERROR | Task exception was never retrieved
python3[1738237]: future: <Task finished name='Task-3' coro=<QemuVM.stop() done, defined at /opt/aleph-vm/aleph/vm/hypervisors/qemu/qemuvm.py:180> exception=AttributeError("'QemuConfidentialVM' object has no attribute 'journal>
python3[1738237]: Traceback (most recent call last):
python3[1738237]:   File "/opt/aleph-vm/aleph/vm/hypervisors/qemu/qemuvm.py", line 184, in stop
python3[1738237]:     if self.journal_stdout and self.journal_stdout != asyncio.subprocess.DEVNULL:
python3[1738237]:        ^^^^^^^^^^^^^^^^^^^

Related ClickUp, GitHub or Jira tickets : ALEPH-517

Self proofreading checklist

• The new code clear, easy to read and well commented.
• New code does not duplicate the functions of builtin or popular libraries.
• An LLM was used to review the new code and look for simplifications.
• New classes and functions contain docstrings explaining what they provide.
• All new code is covered by relevant tests.
• Documentation has been updated regarding these changes.
• Dependencies update in the project.toml have been mirrored in the Debian package build script packaging/Makefile