MiNiFi C2 Flow update - Queue is dropped even component exists in the proposed flow

Issue

When we propose a new flow for a running MiNiFi instance it first stop the source processors and try to wait until a pre-defined graceful period to have empty queues. If remaining items are in the queues after this period, the given flowfiles are dropped.

This behaviour may cause data loss if the proposed flow contains some existing components.

Proposed solution

After the graceful period expires, we should drop flowfiles only from those queues, that don't exist in the proposed flow.