While writing runc test cases to verify that runc correctly uses RPC
configuration files it became clear that some things were not working as
they are supposed to. Looking closer at the code to set log files
via RPC configuration files I discovered that the code seems wrong (at
least I did not understand it any more (or the intentions behind it)).

This code tries to simplify that logic a bit and add more comments to
make clear what the intentions of the RPC configuration file code is.

v2:
  - fix existing test case to test better (more correct)
  - make changes requested by Andrei
v3:
  - more changes as requested by Andrei
Signed-off-by: Adrian Reber <areber@redhat.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>