Fact parser flag keep_subnet to prevent subnet override during fact upload
Setting "Update subnets from facts" makes discovery impossible if taxonomy does not match the host leading to "Subnet is not defined for host's organization". Discovery uses standard core Puppet parser to recognize all interfaces, therefore discovery users must have all subnet taxonomy aligned with discovered host taxonomy, even if they don't plan to use all interfaces.
This patch adds flag keep_subnet which is added by discovery, when present subnet is never updated. This prevents the misbehavior when the flag is set.