[hack] Don't swallow exceptions silently when using Daemon.fork
[hack] Don't swallow exceptions silently when using Daemon.fork

Summary:D2890078 switched spawn to fork which made our errors disappear from logs.

When using Daemon.spawn the exceptions and backtrace go to stderr: diffusion/FBCODE/browse/master/hphp/hack/src/utils/daemon.ml;584dafefbaa24354c308363fbb3a7cf533917e1b$140-141
Do the same for Daemon.fork.

Reviewed By: int3

Differential Revision: D2969096

fb-gh-sync-id: 49192d4c136d26a9f688602e753143861cccfa2c
shipit-source-id: 49192d4c136d26a9f688602e753143861cccfa2c

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