gpuservice: prevent hang in destruction

When initialization of bpf programs fail, the threads
here hang for 30s, which is too long to fuzz.

We can stop them, so the fuzzer progresses (and sometimes
hits the 1s timeout), but at least this is better.

Without this patch, on CF, the error that is occurring is:
> Failed to attach bpf program to power/gpu_work_period tracepoint [2(No such file or directory)]

Fixes: 318008019
Test: gpu_service_fuzzer

Change-Id: I0f2dbf911970f3cd5c736a5cd1697accc1e95937