OpenBSD fixes

Hi,

Several fixes to get puppetdb to install on OpenBSD:
- set @plibdir for the terminus code
- add an init script for OpenBSD's rc.d
- drop -T from ln(1)

The first two changes don't affect non-OpenBSD, however the third one does. -T isn't specified by POSIX as being a mandatory option and it appears to be a GNU extension. Is there any particular reason to use -T, as it works fine without. The code could be adjusted with a small check for @operatingsystem and drop -T on non-Linux if that's desireable.