Flaky test: provisioningserver.drivers.pod.tests.test_lxd.TestLXDPodDriver.test_power_on_noop_if_on

[Igor Brovtsin]

Caught while merging https://code.launchpad.net/~igor-brovtsin/maas/+git/maas/+merge/449935 that doesn't have any changes related to the test. The test runner output follows:

```
======================================================================
FAIL: provisioningserver.drivers.pod.tests.test_lxd.TestLXDPodDriver.test_power_on_noop_if_on
provisioningserver.drivers.pod.tests.test_lxd.TestLXDPodDriver.test_power_on_noop_if_on
----------------------------------------------------------------------
testtools.testresult.real._StringException: testtools.testresult.real._StringException: Empty attachments:
  Twisted logs
  twisted-log

Seeds: {{{MAAS_RAND_SEED=7a6837235e8dce79 PYTHONHASHSEED=3435069977}}}
traceback-1: {{{
Traceback (most recent call last):
  File "/run/build/checkout/src/provisioningserver/certificates.py", line 56, in from_pem
    key = crypto.load_privatekey(
  File "/usr/lib/python3/dist-packages/OpenSSL/crypto.py", line 2939, in load_privatekey
    _raise_current_error()
  File "/usr/lib/python3/dist-packages/OpenSSL/_util.py", line 57, in exception_from_error_queue
    raise exception_type(errors)
OpenSSL.crypto.Error: [('DECODER routines', '', 'unsupported')]

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/run/build/checkout/.ve/lib/python3.10/site-packages/fixtures/fixture.py", line 196, in setUp
    self._setUp()
  File "/run/build/checkout/src/provisioningserver/testing/certificates.py", line 33, in _setUp
    cert = Certificate.from_pem(self.cache_path.read_text())
  File "/run/build/checkout/src/provisioningserver/certificates.py", line 61, in from_pem
    raise CertificateError("Invalid PEM material")
provisioningserver.certificates.CertificateError: Invalid PEM material

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/run/build/checkout/.ve/lib/python3.10/site-packages/fixtures/fixture.py", line 207, in setUp
    raise SetupError(details)
fixtures.fixture.SetupError: {}
}}}

Traceback (most recent call last):
  File "/run/build/checkout/src/provisioningserver/certificates.py", line 56, in from_pem
    key = crypto.load_privatekey(
  File "/usr/lib/python3/dist-packages/OpenSSL/crypto.py", line 2939, in load_privatekey
    _raise_current_error()
  File "/usr/lib/python3/dist-packages/OpenSSL/_util.py", line 57, in exception_from_error_queue
    raise exception_type(errors)
OpenSSL.crypto.Error: [('DECODER routines', '', 'unsupported')]

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/run/build/checkout/.ve/lib/python3.10/site-packages/fixtures/fixture.py", line 196, in setUp
    self._setUp()
  File "/run/build/checkout/src/provisioningserver/testing/certificates.py", line 33, in _setUp
    cert = Certificate.from_pem(self.cache_path.read_text())
  File "/run/build/checkout/src/provisioningserver/certificates.py", line 61, in from_pem
    raise CertificateError("Invalid PEM material")
provisioningserver.certificates.CertificateError: Invalid PEM material
```