create acceptance to ensure client does not overwrite server-set variables

from the parent (quoting henrik.lindberg):

After discussion with Eric Soerenson, we decided that it was best to make this an opt-in and that we are not adding a function - this for the sake of consistency between $facts, $trusted_facts, and $server_facts. This means:

• At the same place where we currently set $trusted_facts we should also set $server_facts if users have opted in
• The values set in $server_facts are the @server_facts set in the node by the compiler indirection + the current environment name
• The user opts in by using the setting :trusted_server_facts
• The setting is false by default
• We issue a warning if any node parameter is overwritten

QA Risk Analysis

N/A for testing tickets