VU: cannot remove old services, cannot override paths

[cmars]

It's currently not possible to remove a service from VU aggregation. This is a problem if you break one service into two or more and want to aggregate them into a compiled API. The prior monolith will conflict forever with the new services because the storage implementations pull in all the old versions of the old service and it claims all the paths.

It's also not possible to selectively say:

• Aggregate everything from Old Monolith service except /path1, /path2 and /path3 which we moved to Shiny New Service
• Aggregate everything from Shiny New Service

It's also not possible to maintain historical continuity if the service scrape URL changes.

In order to be able to use VU in a dynamic services world, we need several things to happen:

• Stop collating services into the result aggregate specs that have been removed from the scrape list.
• Stop identifying services by their hostname in storage, but instead use a logical name. Logical name points at a hostname which can then change without disrupting history.
• Path matching patterns per service to limit what gets merge from each service. We probably need both include and exclude patterns for this...