Fix agent PXE template

This regressed when the iLO/agent code landed. This commit:
* Fixes the template
* Adds a test for the agent PXE template
* Removes unused parameter ipa-advertise-url from the template

Change-Id: I41a0189ce5d14e1f1e6b7be9872d029e157fe3c2
Merge "Fix agent PXE template"