Add a dry-run option to onedb fsck command

[brodriguez-opennebula]

Description
Currently it is impossible to know the changes that onedb fsck will make in the database until it is run and they have to be done with the opennebula service stopped (RW mode). A --dry-run option on the onedb fsck command would allow to check previously if there will be any change.

Use case
Auditing changes and avoid opennebula downtimes (service has to be stopped to run onedb fsck)

• OpenNebula administrator needs to audit which changes have to be done to the DB
• Administrator runs onedb fsck --dry-run without needing to stop OpenNebula's DB
• The command outputs the changes that would be done on a onedb fsck
• The administrator can consider if onedb fsck has to be run in advance

Interface Changes
Do not aply

Additional Context
Do not apply

Progress Status

• Code committed
• Testing - QA
• Documentation (Release notes - resolved issues, compatibility, known issues)