The update prepare command returned an error when setting with this syntax.

Waiting for messages on queue 'tripleo' with no timeout.
Action tripleo.parameters.update execution failed: Error validating environment for plan ocd03: ERROR: The Parameter (DockerPuppetProcessCount) was not defined in template.
Traceback (most recent call last):

  File "/usr/lib/python2.7/site-packages/heat/common/context.py", line 422, in wrapped
    return func(self, ctx, *args, **kwargs)

  File "/usr/lib/python2.7/site-packages/heat/engine/service.py", line 1263, in validate_template
    validate_res_tmpl_only=True)

  File "/usr/lib/python2.7/site-packages/osprofiler/profiler.py", line 158, in wrapper
    result = f(*args, **kwargs)

  File "/usr/lib/python2.7/site-packages/heat/engine/stack.py", line 849, in validate
    validate_value=self.strict_validate)

  File "/usr/lib/python2.7/site-packages/heat/engine/parameters.py", line 535, in validate
    self._validate_user_parameters()

  File "/usr/lib/python2.7/site-packages/heat/engine/parameters.py", line 577, in _validate_user_parameters
    raise exception.UnknownUserParameter(key=param)

UnknownUserParameter: The Parameter (DockerPuppetProcessCount) was not defined in template.

Started Mistral Workflow tripleo.validations.v1.check_pre_deployment_validations. Execution ID: a08b8d93-77fd-4019-b95a-68bd20b98c7c
Removing the current plan files
Uploading new plan files
Started Mistral Workflow tripleo.plan_management.v1.update_deployment_plan. Execution ID: 55571a49-4fc7-4ff7-bff4-883fbf7a20c0
Plan updated.
Processing templates in the directory /tmp/tripleoclient-elLka5/tripleo-heat-templates

real    2m41.095s
user    0m5.507s
sys     0m1.219s

Setting it like below did not present the error:
parameter_defaults:
    DockerPuppetProcessCount: 8

Reported by: rhn-support-nalmond

https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/13/html/keeping_red_hat_openstack_platform_updated/assembly-updating_the_overcloud#annotations:58104ac0-7e2e-4412-a896-20d29f0f1095