Merge changes from topic 'debuggerd_ambient'

* changes:
  debuggerd_handler: don't use clone(..., SIGCHLD, ...)
  crash_dump: drop capabilities after we ptrace attach.
  crash_dump: use /proc/<pid> fd to check tid process membership.
  debuggerd_handler: raise ambient capset before execing.
  Revert "Give crash_dump CAP_SYS_PTRACE."