Flask Manager sometimes fails to start

[plasorak]

As evidenced in a recent integration test run, where the hsi-controller exits, and outputs:

SSHPM: Starting process 2987572 on host daq.fnal.gov as user dunedaq
[2025/02/25 09:22:11] INFO       child_node.py:116              drunc.controller.child_node:                  Child hsi-fake-01 is of type ControlType.REST_API and has the URI 131.225.193.20:33315
[2025/02/25 09:22:11] INFO       child_node.py:116              drunc.controller.child_node:                  Child hsi-fake-to-tc-app is of type ControlType.REST_API and has the URI 131.225.193.20:55533
[2025/02/25 09:22:21] CRITICAL   flask_manager.py:123           drunc.utils.response-listener-flaskmanager-fl Cannot ping the response-listener-flaskmanager!
[2025/02/25 09:22:21] CRITICAL   flask_manager.py:124           drunc.utils.response-listener-flaskmanager-fl This can happen if the web proxy is on at NP04.
Exit NanoRC and try again after executing:
source ~np04daq/bin/web_proxy.sh -u
Exception in thread response-listener-flaskmanager:
Traceback (most recent call last):
  File "/cvmfs/dunedaq.opensciencegrid.org/spack/externals/ext-v2.2/spack-0.22.0/opt/spack/linux-almalinux9-x86_64/gcc-13.2.0/python-3.10.10-exmgi46zlajiwa7uqdczwzkcec5yjo4v/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
    self.run()
  File "/cvmfs/dunedaq-development.opensciencegrid.org/nightly/NFD_DEV_250225_A9/.venv/lib/python3.10/site-packages/drunc/utils/flask_manager.py", line 197, in run
    self._create_and_join_flask()
  File "/cvmfs/dunedaq-development.opensciencegrid.org/nightly/NFD_DEV_250225_A9/.venv/lib/python3.10/site-packages/drunc/utils/flask_manager.py", line 188, in _create_and_join_flask
    self.flask = self._create_flask()
  File "/cvmfs/dunedaq-development.opensciencegrid.org/nightly/NFD_DEV_250225_A9/.venv/lib/python3.10/site-packages/drunc/utils/flask_manager.py", line 127, in _create_flask
    raise CannotStartFlaskManager(f"Cannot start a FlaskManager for {self.name}")
drunc.utils.flask_manager.CannotStartFlaskManager: Cannot start a FlaskManager for response-listener-flaskmanager