Currently hub allows managers to exchange programs from corpus.
But reproducers are not exchanged and we don't know if a crash
happens on other managers as well or not.
Allow hub to exchange reproducers.
Reproducers are stored in a separate db file with own sequence numbers.
This allows to throttle distribution of reproducers to managers,
so that they are not overloaded with reproducers and don't lose them on restarts.
Based on patch by Andrey Konovalov:
https://github.com/google/syzkaller/pull/325Fixes#282
Currently hub sends all inputs on first manager connect.
This can be 100K+ inputs and can take long time
and consume tons of memory. Send inputs in 1K parts.
Also increase rpc timeouts as hub still has global mutex.
If hub hangs, it causes all managers to hang as well as they call
hub under the global mutex. So move common rpc code into rpctype
and make it more careful about timeouts (tcp keepalives, call timeouts).
Also don't call hub under the mutex, the call can be slow.
