Description: agent.iso is created in case of empty or invalid rendezvousIP

Here is the content of agent-config.yaml
Empty Case:
--------------------------------------------
kind: AgentConfig
metadata:
  name: sno-cluster
spec:
  rendezvousIP: 
--------------------------------------------
Invalid IP Address Case:
--------------------------------------------
kind: AgentConfig
metadata:
  name: sno-cluster
spec:
  rendezvousIP: 12121221
--------------------------------------------

How reproducible:

always

Repro Steps: 

1) Get the latest agent-installer and build

git clone -b agent-installer https://github.com/openshift/installer.git
cd installer/
hack/build.sh

2) Create agent.iso using agent-config and install-config files.


Expected: Installer should be thrown an error message something like this: spec.rendezvousIP: Invalid value: “”: rendezvousIP must provide the valid IP address.
Actual: Able to create agent.iso image.