Add new machine guix-hpc8.

• build-node.scm, head-node.scm: Add key file entry for guix-hpc8.
• deploy.scm: Add entry for guix-hpc8.
• guix-hpc8.scm, guix/keys/guix-hpc8.pub: New files.

requested review from @lcourtes

assigned to @rgarbage

approved this merge request

added 7 commits

• 62942577...593cc027 - 6 commits from branch guix-hpc:master
• a78ee24f - Add new machine guix-hpc8.

Compare with previous version

merged