[iu-glints]

• Fix ERR_HTTP_HEADERS_SENT when an asset request arrives during recompilation. webpack-dev-middleware can fulfill its promise after queueing the request, before writing the response. The previous adapter then let Hapi send a response first.
• Wait for middleware next() or response finish/close. Remove listeners on settlement and handle synchronous throws, rejected promises, callback errors, and response errors.
• Use the same adapter for hot middleware so disconnected event streams release the pending Hapi lifecycle.
• Add real Hapi/Webpack regression coverage for bulk file edits and concurrent asset requests, plus lifecycle/error cases. Run the suite in CI against development middleware 6.1.1.

Asset arrives during rebuild
  Webpack queues the request
  Hapi waits
  Webpack serves the rebuilt asset
  Adapter returns h.abandon

Task: MON-146045