Set hostname explicitly in user data during cloud-init for proxy nodes

Closes #244

Issue: When we query the node exporter endpoint, we noticed that the nodename from http-proxy and ood-gpfs5 have hash at the end which is different from ssh-proxy.

172.20.10.32 ssh-proxy

172.20.10.6 http-proxy-edbc74b

Fix: We've seen that cloud_init tries to overwrite the nodename with the nodename provided by the user as a CI argument, however after multiple attempts, it still fails.

Issue stems from packer adding a tag to the build image name as an artifact which does not seem to be overwritten by cloud_init, hence the proposed solution fixes the packer build image name by forcing/overwriting it with the hostnamectl command