Description: unable to create agent.iso when providing agent-config and manifests files (including nmstateconfig.yaml) together.

Here is the content of agent-config.yaml
--------------------------------------------
kind: AgentConfig
metadata:
  name: sno-cluster
spec:
  rendezvousIP: 192.168.111.80
  hosts:
    - hostname: master-0
      role: master
      rootDeviceHints:
       deviceName: /dev/sdb
      interfaces:
       - name: eno1
         macAddress: 00:ef:44:21:e6:a5
--------------------------------------------

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 all manifests files including nmstateconfig.


Expected: Agent.iso should be created without any issue.
Actual: Unable to create agent.iso image, below are the logs:

INFO[0001] Start configuring static network for 1 hosts  pkg=manifests
ERRO[0001] <nmstatectl gc> failed, errorCode 1, stderr Traceback (most recent call last):
  File "/usr/bin/nmstatectl", line 11, in <module>
    load_entry_point('nmstate==1.2.1', 'console_scripts', 'nmstatectl')()
  File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 74, in main
    return args.func(args)
  File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 390, in run_gen_config
    if statedata[0] == "{":
IndexError: string index out of range
, input yaml <>  pkg=manifests
ERRO[0001] Failed to create static config for host       error="<nmstatectl gc> failed, errorCode 1, stderr Traceback (most recent call last):\n  File \"/usr/bin/nmstatectl\", line 11, in <module>\n    load_entry_point('nmstate==1.2.1', 'console_scripts', 'nmstatectl')()\n  File \"/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py\", line 74, in main\n    return args.func(args)\n  File \"/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py\", line 390, in run_gen_config\n    if statedata[0] == \"{\":\nIndexError: string index out of range\n, input yaml <>" pkg=manifests
ERROR failed to write asset (Agent Installer ISO) to disk: image reader not available 
FATAL failed to fetch Agent Installer ISO: failed to fetch dependency of "Agent Installer ISO": failed to generate asset "Agent Installer Ignition": failed to create StaticNetwork config data: <nmstatectl gc> failed, errorCode 1, stderr Traceback (most recent call last): 
FATAL   File "/usr/bin/nmstatectl", line 11, in <module> 
FATAL     load_entry_point('nmstate==1.2.1', 'console_scripts', 'nmstatectl')() 
FATAL   File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 74, in main 
FATAL     return args.func(args)                   
FATAL   File "/usr/lib/python3.6/site-packages/nmstatectl/nmstatectl.py", line 390, in run_gen_config 
FATAL     if statedata[0] == "{":                  
FATAL IndexError: string index out of range        
FATAL , input yaml <>