When scaling up, new nodes don't appear in `/etc/hosts`

Issue

• When scaling up, new nodes don't appear in /etc/hosts and the following error is seen is /var/log/messages:

Nov 22 10:34:03 overcloud-compute-100 os-collect-config: [2019-11-22 10:34:02,900] (heat-config) [INFO] deploy_signal_id=http://10.10.10.10:8000/v1/signal/arn%3Aopenstack%3Aheat%3A%3A02f43d3011594af1a9f1c0c7021bdacc%3Astacks/overcloud-Compute6-hbHostsDeployment-c6uiqkw3fnya/d0043a71-4846-427e-be2c-9995c7c050d6/resources/3?Timestamp=2019-11-22T15%3A33%3A18Z&SignatureMethod=HmacSHA256&AWSAccessKeyId=f8e0569858324490a41353397fbed354&SignatureVersion=2&Signature=2jDxn3HVvCzbD59BeTAs0kUFPWxxSLiaEXD4UMeAIfc%3D
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: [2019-11-22 10:34:02,901] (heat-config) [INFO] deploy_signal_verb=POST
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: [2019-11-22 10:34:02,901] (heat-config) [DEBUG] Running /var/lib/heat-config/heat-config-script/213767fe-9176-43bf-b5b5-0f489df7247b
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: Traceback (most recent call last):
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: File "/usr/libexec/heat-config/hooks/script", line 96, in <module>
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: sys.exit(main(sys.argv))
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: File "/usr/libexec/heat-config/hooks/script", line 66, in main
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: stderr=subprocess.PIPE, env=env)
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: File "/usr/lib64/python2.7/subprocess.py", line 711, in __init__
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: errread, errwrite)
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: File "/usr/lib64/python2.7/subprocess.py", line 1327, in _execute_child
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: raise child_exception
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: OSError: [Errno 7] Argument list too long
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: [2019-11-22 10:34:02,908] (heat-config) [ERROR] Error running /usr/libexec/heat-config/hooks/script. [1]
Nov 22 10:34:03 overcloud-compute-100 os-collect-config: [2019-11-22 10:34:02,908] (heat-config) [DEBUG] Running heat-config-notify /var/lib/heat-config/deployed/213767fe-9176-43bf-b5b5-0f489df7247b.json < /var/lib/heat-config/deployed/213767fe-9176-43bf-b5b5-0f489df7247b.notify.json
Nov 22 10:34:04 overcloud-compute-100 systemd: Created slice User Slice of heat-admin.