Cannot remotely change node registration from "pattern" to "policy".

[TheMosquito]

Although you can change the node's pattern remotely, and change the node's policy remotely, you cannot:

• change the node from using a pattern to using a policy
• remove a pattern from a node to enable later re-registration with policy

This caused a significant problem in the field when an Open Horizon node was registered with a pattern but then when it was on site at a conference venue, behind 2 firewalls, it could not be changed to use policy since the node could not be reached by ssh. Note that this would also be required before we can deprecate patterns.