The "my virtual machines" page showed "We could not load your VMs due to a
backend connection error" for any user owning a VM whose template had been
removed from OpenNebula. OpenNebulaManager.get_template() converted every
failure, including WrongIdError for a missing template, into
ConnectionRefusedError, and VirtualMachineSerializer.get_configuration()
let that propagate, so one VM with a stale template id took down the whole
list. The only log output was an empty ERROR line, because WrongIdError
has no message.
* Add opennebula_api.exceptions.TemplateNotFoundError and raise it from
get_template() for a missing template; keep ConnectionRefusedError for
genuine backend failures and log them with a traceback.
* Add OpenNebulaManager.get_template_names() and resolve_template_id() so
the serializer fetches the template pool once per list instead of
constructing an OpenNebulaManager and fetching the pool for every VM.
* get_configuration() now falls back to the template name embedded in the
VM name ("<template>-<vm id>") when the template is missing or the pool
cannot be fetched, and logs why.
* Replace str.lstrip('public-') with a real prefix strip (lstrip removes a
character set, so "public-ubuntu" became "ntu") and also strip
"ipv6only-".
* ProcessVMSelectionMixin shows "configuration is no longer available"
instead of an unhandled error when ordering a retired template.
* VirtualMachinesPlanListView logs the exception behind the banner.
* Add mock-based unit tests for the fallback, the UPDATED_TEMPLATES
mapping, the single pool fetch and the new exception.
The UPDATED_TEMPLATES setting keeps working as an operational override for
mapping retired template ids to their replacements.
