AS-88: Scheduler reset to new path

This is subset of #573 that adds `reset` in current scheduler without any sub-process change. We can merge this first, use it for a while and then go back to that PR when we really need to debug kazoo's partitioning recipe. This change will allow partitioning to start in new path via sending `POST /scheduler_reset?path=/new_path` to otter. 

https://jira.rax.io/browse/AS-88