runsc: Fix map access race in boot.Loader.waitContainer.
runsc: Fix map access race in boot.Loader.waitContainer.

PiperOrigin-RevId: 204522004
Change-Id: I4819dc025f0a1df03ceaaba7951b1902d44562b3

google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor,google/gvisor