Fix logdev checking on Debian Jessie

Irker expects only one of (`/dev/log`, `/var/run/syslog`,
`/var/run/log`) to exist, however on Debian Jessie, we’ve got
`/var/run/log` (which is a directory), too.

See merge request !1

Irker expects only one of ('/dev/log', '/var/run/syslog',
'/var/run/log') to exist, however on Debian Jessie, we’ve got
/var/run/log (which is a directory), too.