syz-manager: speed up crash reading
syz-manager: speed up crash reading

Currently we read lots of unnecessary files. This is slow on GCE.
Read only necessary info.
For summary report use on readdirnames (which does not do stat on every file).
For detailed crash report read additional info, but only for this crash.

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