Verify validation for PNF manifest parameter onap_pnf_sw_version

Verify that https://jira.onap.org/browse/VNFSDK-531 works properly.

CoS:

PNF onboarding package validation is improved with onap_pnf_sw_version artifact-set check, as well as a "PNF sw-version" file contents check.
onap_pnf_sw_version artifact set is optional in meta data file.
Details: https://jira.onap.org/browse/VNFSDK-531
However, if onap_pnf_sw_version is present, then the following shall be validated:
The File(s) mentioned under the onap_pnf_sw_version must exist
The File(s) mentioned under the onap_pnf_sw_version must have the yaml format and file extension
The File(s) mentioned under the onap_pnf_sw_version must contain at least following information:
pnf_software_information: (YAML tag)
pnf_software_version: “<version>” (YAML key,value)
Check, if a new validation class was created and is attached to the list of all PNF validations - for Frankfurt release
Check, if the jUnit tests are updated accordingly (use a new CSAR, covering positive/negative cases).
Make sure VNF validations (TOSCA variant) are not affected by this modification.