upgrade to 0.5.1 is hard due to certificates already being in mongo

we had a quick chat about this and believe the end state should be:

• all three possible certs (root, doorman and network map) should be stored on the filesystem going forwards
  • nb this is mainly to make life easier for kube people
• upgrade will be supported by providing a tool to extract these from existing mongo into files
  • it's your call how you then get these into an upgaded nms deployment
• the storage flag default has changed to filesystem - either fix this or fix docs
• we need to make it clear that cert storage is never in mongo going forwards