syz-manager: improve vm management during repro
syz-manager: improve vm management during repro

1. Don't start reproducing crashes until we triage
   all inputs from corpus and hub. This minimizes
   chances of losing inputs from hub. Also allows
   to faster get idea of total coverage.
2. Fix bug when vmCount%instacesPerRepro != 0.
   Currently we stop the remainder of instances
   and it stays idle.

google/syzkaller,zoulasc/syzkaller,dotweiba/syzkaller,xairy/syzkaller,xairy/syzkaller,xairy/syzkaller,zoulasc/syzkaller,google/syzkaller,zoulasc/syzkaller,hyz0906/syzkaller,hyz0906/syzkaller,hyz0906/syzkaller,google/syzkaller,dotweiba/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,dotweiba/syzkaller,dotweiba/syzkaller,xairy/syzkaller,xairy/syzkaller,hyz0906/syzkaller,google/syzkaller,hyz0906/syzkaller,zoulasc/syzkaller,google/syzkaller