Custom FS freeze operation for live cpds

[rsmontero]

Description When a disk is saved-as into the datastore the TM driver issue some KVM/libvirt commands to perform a save copy (blockcp/somfsfreeze)...

This operations are hypervisor specific and the driver needs to expose a modular interface to implement custom fs-freeze/unfreeze operations. Current affected operations are:

• ceph/cpds.ssh
• qcow2/cpds
• qcow2/cpds.ssh
• ssh/cpds

Use case Save disk-saveas operations across hypervisors

Interface Changes TM driver need to hook on specific KVM/LXC/FC freeze operations

Additional Context

Progress Status

• [ ] Branch created
• [ ] Code committed to development branch
• [ ] Testing - QA
• [ ] Documentation
• [ ] Release notes - resolved issues, compatibility, known issues
• [ ] Code committed to upstream release/hotfix branches
• [ ] Documentation committed to upstream release/hotfix branches

[rsmontero]

Consider this together with: #5463