Use daemon module for the plugin backend

Previous manual daemonize wouldn't work because it wasn't POSIX
compliant, only one fork() was being called and no file descriptors were
being copied.

Merge:	releng/9.1.0
(cherry picked from commit c472eb374683538aa1d6a28be730f551e1b72d1f)

Conflicts:
	nanobsd/plugins/firefly_pbi/pbi.conf
Use daemon module for transmission as well

Merge:	releng/9.1.0
(cherry picked from commit a6957dd754174dfeb1fc2146a41ce34cc9c54aee)

Conflicts:
	nanobsd/plugins/transmission_pbi/pbi.conf