[VMware to KVM Migration] Fix for converted instance NPE issue when source VMware instance OVF is exported from management server

[sureshanaparti]

Description

This PR fixes converted instance NPE issue in VMware to KVM Migration when source VMware instance OVF is exported from management server.

Fixes #10982

Some of the changes of the below PRs were missing in 4.20, resulting in NPE.

• https://github.com/apache/cloudstack/pull/9787
• https://github.com/apache/cloudstack/pull/9764
• https://github.com/apache/cloudstack/pull/10409

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
• [x] Major
• [ ] Minor
• [ ] Trivial

Screenshots (if appropriate):

How Has This Been Tested?

Tested VMware instance migration to KVM, without ovftool installation on KVM hosts. OVF of source VMware instance is downloaded from Management Server.

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