Bugfixes for the dnf plugin

[stevenbrz]

• Point to the correct fifo path (as referenced in paths.h)
• Write a newline to get fapolicyd to pick up the write

cc. @kenbreeman

[radosroka]

Thank you for the contribution. I totally forgot to add a new line there.

If you can you should use rpm-plugin instead of dnf one.

https://github.com/rpm-software-management/rpm/blob/master/plugins/fapolicyd.c

[stevenbrz]

This is the first I've heard of the rpm plugin - after testing it looks like exactly what we need here, thanks!