AthenaCommon: Ensure ptrace of athena is allowed.

On kernels with Yama enabled, ptrace may not work by default on processes which are not decendants of the tracing process. Among other things, that causes the way we attach the debugger to fail. However, we can disable this on a per-process basis. So do that when we initialize Athena.

See https://www.kernel.org/doc/Documentation/security/Yama.txt and prctl(2).