[programs/cluido] Be less hard-wired as to which servers are started

[perlun]

chaos is, by design, a microservice architecture. We decided to, once and for all, slay the monolith and this affects all of the system in "a great many things".

However, sometimes we have been a bit sloppy in making things presume other things being present and this is not good. For example, the pci command in cluido - it currently fails with a "mailbox 0 could not be found" if you attempt to use it when the pci server is not started. Of course it should be possible to run a chaos system without PCI (even though such a configuration is odd).

So: cluido should try to resolve the pci service, and if it is not found, gracefully handle that scenario.