Don't allow NAS backup for vm with encrypted volumes

### problem

Don't allow backup for vm with encrypted volumes

### versions

ACS 4.22

### The steps to reproduce the bug

1. Configure the backup.framework.provider.plugin to nas
2. Launch a vm and assign a backup offering
3. Take a backup of the encrypted vm
4. Try to create an instance from the backup

5. Exception observed

```
2026-05-20 05:46:29,634 WARN [resource.wrapper.LibvirtStartCommandWrapper] (AgentRequest-Handler-5:[]) (logid:ae054c8c) LibvirtException org.libvirt.LibvirtException: internal error: qemu unexpectedly closed the monitor: 2026-05-20T05:46:29.444365Z qemu-kvm: -blockdev {"node-name":"libvirt-3-format","read-only":false,"cache":{"direct":true,"no-flush":false},"driver":"qcow2","encrypt":{"format":"luks","key-secret":"libvirt-3-format-encryption-secret0"},"file":"libvirt-3-storage","backing":null}: No encryption in image header, but options specified format 'luks'
at org.libvirt.ErrorHandler.processError(Unknown Source)
at org.libvirt.ErrorHandler.processError(Unknown Source)
at org.libvirt.Connect.domainCreateXML(Unknown Source)
at com.cloud.hypervisor.kvm.resource.LibvirtComputingResource.startVM(LibvirtComputingResource.java:2241)
at com.cloud.hypervisor.kvm.resource.LibvirtComputingResource.startVM(LibvirtComputingResource.java:2210)
at com.cloud.hypervisor.kvm.resource.wrapper.LibvirtStartCommandWrapper.execute(LibvirtStartCommandWrapper.java:91)
at com.cloud.hypervisor.kvm.resource.wrapper.LibvirtStartCommandWrapper.execute(LibvirtStartCommandWrapper.java:52)
at com.cloud.hypervisor.kvm.resource.wrapper.LibvirtRequestWrapper.execute(LibvirtRequestWrapper.java:78)
at com.cloud.hypervisor.kvm.resource.LibvirtComputingResource.executeRequest(LibvirtComputingResource.java:2280)
at com.cloud.agent.Agent.processRequest(Agent.java:813)
at com.cloud.agent.Agent$AgentRequestHandler.doTask(Agent.java:1295)
at com.cloud.utils.nio.Task.call(Task.java:83)
at com.cloud.utils.nio.Task.call(Task.java:29)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
at java.base/java.lang.Thread.run(Thread.java:840)

```

6. Stop the vm

7. Restore the vm to backup > Exception observed

8. Vm is unable to start due to insufficent capacity even , not sure why this error comes when there is enough capacity

```
2026-05-20 06:19:16,470 DEBUG [c.c.d.DeploymentPlanningManagerImpl] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331, ctx-8fad60d0]) (logid:d156b428) DeploymentPlan [DataCenterDeployment] has specified host [1] without HA flag. Choosing this host to deploy VM [VM instance {"id":24,"instanceName":"i-2-24-VM","state":"Starting","type":"User","uuid":"e2ae52ce-4249-4772-b789-26f566cbe52f"}].
2026-05-20 06:19:16,470 DEBUG [c.c.d.DeploymentPlanningManagerImpl] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331, ctx-8fad60d0]) (logid:d156b428) Cannot deploy VM [VM instance {"id":24,"instanceName":"i-2-24-VM","state":"Starting","type":"User","uuid":"e2ae52ce-4249-4772-b789-26f566cbe52f"}] to host [Host {"id":1,"name":"ref-trl-11676-k-Mol8-kiran-chavala-kvm1","type":"Routing","uuid":"71c97b41-2f20-4576-9e1f-110cdf73fbb4"}] because this host is in the avoid set.
2026-05-20 06:19:16,484 DEBUG [c.c.c.CapacityManagerImpl] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331, ctx-8fad60d0]) (logid:d156b428) VM instance {"id":24,"instanceName":"i-2-24-VM","state":"Stopped","type":"User","uuid":"e2ae52ce-4249-4772-b789-26f566cbe52f"} state transited from [Starting] to [Stopped] with event [OperationFailed]. VM's original host: Host {"id":2,"name":"ref-trl-11676-k-Mol8-kiran-chavala-kvm2","type":"Routing","uuid":"4c8f5777-b8fb-4bf9-ab31-461c2474dd36"}, new host: null, host before state transition: Host {"id":1,"name":"ref-trl-11676-k-Mol8-kiran-chavala-kvm1","type":"Routing","uuid":"71c97b41-2f20-4576-9e1f-110cdf73fbb4"}
2026-05-20 06:19:16,488 DEBUG [c.c.c.CapacityManagerImpl] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331, ctx-8fad60d0]) (logid:d156b428) Hosts's actual total CPU: 6000 and CPU after applying overprovisioning: 12000
2026-05-20 06:19:16,488 DEBUG [c.c.c.CapacityManagerImpl] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331, ctx-8fad60d0]) (logid:d156b428) Hosts's actual total RAM: (6.76 GB) 7259152384 and RAM after applying overprovisioning: (6.76 GB) 7259152384
2026-05-20 06:19:16,488 DEBUG [c.c.c.CapacityManagerImpl] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331, ctx-8fad60d0]) (logid:d156b428) release cpu from host: Host {"id":1,"name":"ref-trl-11676-k-Mol8-kiran-chavala-kvm1","type":"Routing","uuid":"71c97b41-2f20-4576-9e1f-110cdf73fbb4"}, old used: 2500, reserved: 0, actual total: 6000, total with overprovisioning: 12000; new used: 500,reserved:0; movedfromreserved: false,moveToReservered: false
2026-05-20 06:19:16,488 DEBUG [c.c.c.CapacityManagerImpl] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331, ctx-8fad60d0]) (logid:d156b428) release mem from host: Host {"id":1,"name":"ref-trl-11676-k-Mol8-kiran-chavala-kvm1","type":"Routing","uuid":"71c97b41-2f20-4576-9e1f-110cdf73fbb4"}, old used: (2.50 GB) 2684354560, reserved: (0 bytes) 0, total: (6.76 GB) 7259152384; new used: (512.00 MB) 536870912, reserved: (0 bytes) 0; movedfromreserved: false, moveToReservered: false
2026-05-20 06:19:16,498 ERROR [c.c.v.VmWorkJobHandlerProxy] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331, ctx-8fad60d0]) (logid:d156b428) Invocation exception, caused by: com.cloud.exception.InsufficientServerCapacityException: Unable to create a deployment for VM instance {"id":24,"instanceName":"i-2-24-VM","state":"Starting","type":"User","uuid":"e2ae52ce-4249-4772-b789-26f566cbe52f"}Scope=interface com.cloud.dc.DataCenter; id=1
2026-05-20 06:19:16,498 INFO [c.c.v.VmWorkJobHandlerProxy] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331, ctx-8fad60d0]) (logid:d156b428) Rethrow exception com.cloud.exception.InsufficientServerCapacityException: Unable to create a deployment for VM instance {"id":24,"instanceName":"i-2-24-VM","state":"Starting","type":"User","uuid":"e2ae52ce-4249-4772-b789-26f566cbe52f"}Scope=interface com.cloud.dc.DataCenter; id=1
2026-05-20 06:19:16,498 DEBUG [c.c.v.VmWorkJobDispatcher] (Work-Job-Executor-136:[ctx-b060718b, job-330/job-331]) (logid:d156b428) Done with run of VM work job: com.cloud.vm.VmWorkStart for VM 24, job origin: 330

```

### What to do about it?

Validate if the vm disk are encrypted , and don't allow assigning a backup offering to the vm