Allow downgrade in panos_software.py

[nembery]

allow panos_software to perform downgrades in addition to upgrades

Description

panos_software no longer allows the user to perform a software downgrade. This patch allows a downgrade operation by verifying the version sequence. I.e. 1 minor or major step at a time.

Motivation and Context

Downgrades are a requirement that should be supported. If an upgrade fails for some reason, we should be able to use panos_software to rollback.

How Has This Been Tested?

Use panos_software module with a desired version less than the current version

Screenshots (if appropriate)

Types of changes

simple logic to check if desired_version is less than current version by no more than 1

• Bug fix (non-breaking change which fixes an issue)

Not being able to downgrade is a bug that was introduced some time ago.

Checklist

• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes if appropriate.
• [x] All new and existing tests passed.