A node that runs DDL query while its cluster does not have a quorum
cannot be shutdown since the query is not abortable. The series makes it
abortable and also fixes the order in which components are shutdown to
avoid the deadlock.
* gleb/raft_shutdown_v4 of git@github.com:scylladb/scylla-dev.git:
migration_manager: drain migration manager before stopping protocol servers on shutdown
migration_manager: pass abort source to raft primitives
storage_proxy: relax some read error reporting
9fdb49c86a