check_blacklist.sh calls "host" command which is not always present in some containers.

[StevenCTimm]

Describe the bug
The stock factory script check_blacklist.sh calls the unix "host" command which is not available in stock containers.

To Reproduce
Steps to reproduce the behavior:
Run in the stock cms rhel7 or rhel8 shifter container on nersc.
Execute the check_blacklist.sh command in that container
It will error out at line 33 of that script

Expected behavior
Would expect the script to continue and actually process the blacklist if one exists.

Screenshots
If applicable, add screenshots and/or console outputs to help explain your problem.

Info (please complete the following information):
Stakeholders and components can be a comma-separated list or on multiple lines.
If you add a new stakeholder or component, not on the sample list, add it on a line on its own.

• GlideinWMS version: 3.10.6
• Python version: 3.9
• OS version: rhel9
• HTCondor version: 23
• Priority: medium. (this error does not stop the rest of the glidein from starting and running jobs)
• Stakeholders: HEPCloud, DUNE
• Components: Glidein

Additional context
This is not critical as only this script errors out but the rest of the glidein starts up ok.