transient error when relating openstack-hypervisor

[James Page]

I've seen this transient error in the openstack-hypervisor charm a few times during test deployments - I suspect its just a missing guard in the charm code - the RabbitMQ URL is not yet provided.

unit-openstack-hypervisor-1: 09:50:31 ERROR unit.openstack-hypervisor/1.juju-log identity-credentials:7: Exception raised in section 'Bootstrapping': Snap: 'openstack-hypervisor'; command ['snap', 'set', 'openstack-hypervisor', '-t', 'rabbitmq.url=""'] failed with output = ''
unit-openstack-hypervisor-1: 09:50:31 ERROR unit.openstack-hypervisor/1.juju-log identity-credentials:7: Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-openstack-hypervisor-1/charm/lib/charms/operator_libs_linux/v2/snap.py", line 278, in _snap
    return subprocess.check_output(args, universal_newlines=True)
  File "/usr/lib/python3.10/subprocess.py", line 421, in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
  File "/usr/lib/python3.10/subprocess.py", line 526, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['snap', 'set', 'openstack-hypervisor', '-t', 'rabbitmq.url=""']' returned non-zero exit status 1.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/lib/juju/agents/unit-openstack-hypervisor-1/charm/lib/ops_sunbeam/guard.py", line 91, in guard
    yield
  File "/var/lib/juju/agents/unit-openstack-hypervisor-1/charm/lib/ops_sunbeam/charm.py", line 296, in configure_charm
    self.configure_unit(event)
  File "/var/lib/juju/agents/unit-openstack-hypervisor-1/charm/./src/charm.py", line 371, in configure_unit
    self.check_relation_handlers_ready(event)
  File "/var/lib/juju/agents/unit-openstack-hypervisor-1/charm/lib/ops_sunbeam/charm.py", line 244, in check_relation_handlers_ready
    self.stop_services(not_ready_relations)
  File "/var/lib/juju/agents/unit-openstack-hypervisor-1/charm/./src/charm.py", line 495, in stop_services
    self.set_snap_data(snap_data)
  File "/var/lib/juju/agents/unit-openstack-hypervisor-1/charm/./src/charm.py", line 347, in set_snap_data
    hypervisor.set(new_settings, typed=True)
  File "/var/lib/juju/agents/unit-openstack-hypervisor-1/charm/lib/charms/operator_libs_linux/v2/snap.py", line 342, in set
    return self._snap("set", ["-t"] + kv)
  File "/var/lib/juju/agents/unit-openstack-hypervisor-1/charm/lib/charms/operator_libs_linux/v2/snap.py", line 280, in _snap
    raise SnapError(
charms.operator_libs_linux.v2.snap.SnapError: Snap: 'openstack-hypervisor'; command ['snap', 'set', 'openstack-hypervisor', '-t', 'rabbitmq.url=""'] failed with output = ''