Switch to el7 and then to el9 constraint (feature)

[mrcmor100]

The default os in hcswif.py is centos79. The farm is moving to el7 and then to el9. The os feature is not currently a user selected option in hcswif.py
TODO: Update the os default to be el7 (maybe el9) and allow the user to define the os feature as an option on the command line.