Unresolved filename in deploy-mgmt-hub.sh

[elatocki]

I was following the "Deploy All-in-1 Horizon Management Hub, Agent, and CLI" steps in the devops readme for Ubuntu 18.04.
I ran into an issue during the "Downloading template files" step:

Error: http code 000 from: downloading OH_DEVOPS_REPO/mgmt-hub/vault-tmpl.json, stderr: curl: (6) Could not resolve host: OH_DEVOPS_REPO

Looks like this could be avoided by bash-style interpreting the OH_DEVOPS_REPO variable during the template file download. I would be happy to make this change.