Fix mode of /run/libgpod in tmpfiles.d config, use /run consistently
The mode of /run/libgpod was inadvertently set to 0644 in 1c6b028 ("Fix
use of temp files (rhbz#840183), minor other cleanups", 2015-02-11).
Fix this and simply use the tmpfiles.d defaults for mode, uid, and gid.
Replace mixed usage of of /run and /var/run with /run for consistency.
Drop redundant 'mkdir -p %{buildroot}/run' command; install -d creates
all leading path components.