vsts-fullbuild-ubuntu-vm does not support azureps

[vsts-fullbuild-ubuntu-vm](https://github.com/Azure/azure-quickstart-templates/tree/master/vsts-fullbuild-ubuntu-vm)

### Issue Details

Whenever trying to queue a build that includes an azure related build step with this build agent, I get the following message:

> No agent could be found with the following capabilities: azureps

Open the vsts-fullbuild-ubuntu-vm template and inspect how its build agent capabilities are configured. Queue a build containing an Azure-related build step and verify that the agent advertises the azureps capability and is selected successfully.

Written by the indexing model from the issue text.