Provide better handling of failures in GEM port, alloc id removal so that ONU and OLT are in same state

Below  is the gist of the comments made by Gamze Abaka in patch https://gerrit.opencord.org/c/voltha-openolt-adapter/+/30389. Creating this Jira for addressing this particular issue.

We are deleting gemports from the OLT when we call the RemoveSchedulerQueues method. Now, you are deleting a gem port from the cache and sending a gemPortDelete request to the ONU adapter before we delete the gem port from OLT. So, what if the gemport removal operation fails on the OLT? There will be a synchronization problem (ONU adapter will remove the gemport, we already freed the gemport-id but, the gemport will be on the OLT). After that, when we want to provision a new service to another ONU on the same pon port, it will always fail because of the gemport-id allocation. (OLT still uses the gemport for the previous ONU). How will we solve this problem?