add integration test for dispatch logic

Value

• the unit tests for the dispatch module currently rely on a live socket. (ie: the require invoking run and then listening on a socket, when they could simply plass messages into the pure function dispatch.dispatch)
• let's:
  • refactor the dispatch unit tests so they mock everything at the module level and don't invoke run
  • add a "big bracket" (integration) test for the dispatch module that:
    • doesn't mock out the command execution or database layer
    • invokes run, and attempts to test the full execution path for handling a message from coming off the socket from signald to putting messages back on the socket for signald (which we will accomplish by using the new app module to inject a sock resource that receives messages from a testing EventEmitter and writes messages to a stub socket that we can spy on)