Hpnapy

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- Fix: Allow for results that are missing to return an empty result instead of raise an error.
For instance, if a diagnostic is searched and is missing, it will now return an None or empty list.
- Fix: Allow for query results that return a HTTP 201 status code to succeed.

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- Added: New API commands supported:

- add_change_plan
- del_change_plan
- deploy_change_plan
- list_change_plan
- mod_change_plan
- reboot_device
- show_change_plan
- show_rule_compliance
- synchronize

- Fix: HTTP status code 221 causing exception.

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- Fix: HTTP status code 501 causing exception.
- Fix: HTTP status code 204 causing exception.
- Fix: show_policy_compliance was returning a single result when multiple results where expected.