ports-mgmt/poudriere: Make improvements / bug fixes

Fix bug:
1) respect USE_TMPFS and lack thereof (issue 6)
2) respect job limits on slaves (issue 11)

Improvements:
1) Add "jail" directive "-D" to attempt another set of umounts*
2) Automatically bzip2 logs of successful builds and move to another
   directory
3) make a copy of running port failures that can be retrieved with
   new bulk directory "-x".  This can be executed during bulk build

* in case umount fails during ctrl-C or something like that