ccpp_event: pass a list of build ids through pipe instead of file

- 'abrt-action-analyze-core --core=coredump -o build_ids' generates build_ids
  file containing list of build ids found in a core

- '/usr/libexec/abrt-action-install-debuginfo-to-abrt-cache --size_mb=4096'
  installs missing debuginfo for build ids from the list

- the build_ids file is read only by the second binary, the file doesn't have any other  ...

- the build_ids file is generate in analyze_LocalGDB event which is usually run
  in user context, thus file premission looks like this "750 user:user's group"

- abrt-action-install-debuginfo-to-abrt-cache writes to
  /var/cache/abrt-di/usr/lib/debug/.build-id/, therefore it has configured SETUID
  and SETGID bits. So a process has EUID="abrt's uid" and EGID="abrt's gid"

- from the last two points above is obvious that
  abrt-action-install-debuginfo-to-abrt-cache can't read the build_ids file

- the easiest solution is to replace file by pipe

- related to issue #583

Signed-off-by: Jakub Filak <jfilak@redhat.com>