R1:d4bf2a147b7a

Make paths and Aphlict instance names less ambiguous

Summary:
Fixes T10783 (what little of it remains). Ref T10697.

Aphlict currently uses request paths for two different things:

- multi-tenant instancing in the Phacility cluster (each instance gets its own namespace within an Aphlict server);
- some users configure nginx and apache to do proxying or SSL termination based on the path.

Currently, these can collide.

Put a "~" before the instance name to make it unambiguous. At some point we can…