Add presave/postsave and prerestore/postrestore tm actions

[kvaps]

Description
We need this functional for save and restore checkpoint file directly into storage, without saving it into some place before

Use case
Faster save and restore and migrate operations for storage drivers like ceph. And no requirement for additional space to save temprorary file

Interface Changes

• All TM_drivers should implement 4 new actions: presave, postsave, prerestore, postrestore, most of them can be just do exit 0
• Remove save.<TM_MAD> and resotre.<TM_MAD> hooks from vmm-driver

Additional Context
Read the discussion here: https://forum.opennebula.org/t/shared-mode-for-the-ceph-based-system-datastires/7164/13

Working prototype:
https://github.com/kvaps/opennebula-addon-tmsave-tmrestore

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

[atodorov-storpool]

I am closing #3270 and #3271 in favour of #3272 because this solution could be implemented faster and at the moment with a configuration change that does not violate the OpenNebula Polices.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions. The OpenNebula Dev Team

[kvaps]

This is still desirable change.

[atodorov-storpool]

Second for this.
It is already integrated into addon-storpool and is working flawlessly in production setups.