kvm: add SCSI controllers based on the number of virtio-SCSI disks

[weizhouapache]

Description

This PR fixes #7490

According to libvirt code, the units per scsi controller is set to 7 therefore, we need to create scsi controller every 7 disks (including CDROM).

https://github.com/libvirt/libvirt/blob/50cc7a0d9d2b9df085ec073a6d60820a9642158a/src/conf/domain_conf.h#L3007-L3008

https://github.com/libvirt/libvirt/blob/50cc7a0d9d2b9df085ec073a6d60820a9642158a/src/conf/domain_conf.c#L6701-L6704

Types of changes

• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] Enhancement (improves an existing feature and functionality)
• [ ] Cleanup (Code refactoring and cleanup, that may add test cases)
• [ ] build/CI
• [ ] test (unit or integration test code)

Feature/Enhancement Scale or Bug Severity

Feature/Enhancement Scale

• [ ] Major
• [ ] Minor

Bug Severity

• [ ] BLOCKER
• [ ] Critical
• [ ] Major
• [ ] Minor
• [ ] Trivial

Screenshots (if appropriate):

How Has This Been Tested?

How did you try to break this feature and the system with this change?