Fix for CASM-5794: RPM signing key issue

[sajeeshkv-hpe]

symptoms:

During the CSM 1.7.1-p2alpha.3 upgrade prepare-images stage fails with: "Creation of 3 images failed / Bootprep for management nodes failed."
All three management images fail identically (master-secure-kubernetes, worker-secure-kubernetes, storage-secure-storage-ceph).
CFS ansible container log shows the Install RPMs (SLES-based) task failing with:

cfs-trust-1.10.0-1.noarch (CSM No-OS Packages): Signature verification failed
[4-Signatures public key is not available]
warning: cfs-trust-1.10.0-1.noarch.rpm: Header V4 RSA/SHA256 Signature, key ID 19cfb373: NOKEY 

Related PRs

https://jira-pro.it.hpe.com:8443/browse/CASM-5794
https://jira-pro.it.hpe.com:8443/browse/CASMTRIAGE-9262

Pull Request Checklist

• Version number(s) incremented, if applicable
• [x ] Copyrights updated
• [x ] License file intact
• [x ] Target branch correct
• [x ] Testing is appropriate and complete, if applicable
• Release Notes in docs-csm updated, if applicable

[harishkhpe]

LGTM