launcher should be able to run between 0 and n osquery instances

[RebeccaMahany]

We want launcher to be able to run with between 0 and n osquery instances:

1. When launcher can't start osquery, we don't want to restart launcher altogether. This is because, in the case where the current osquery instance is old and not compatible with the current database, it can be helpful for launcher to run for a while with 0 osquery instances so that launcher can reach the autoupdate cycle and self-update its osquery version.
2. In the short term, we want to be able to split up where Kolide queries run versus where tenant queries run, so that if a tenant creates a query that causes issues with osquery, the Kolide queries will still run. (This amounts to running 2 osquery instances.)
3. In the longer term, we want to support multitenant installations. This will mean 1 osquery instance for Kolide queries, and 1 osquery instance per tenant. I propose we refer to these consistently as "Kolide osquery instance" and "tenant osquery instances".

There are a couple steps we need to take to be able to do this. This issue tracks the foundational steps necessary to run 0 or 1 osquery instances.