poudriere blocked after pkg build failed

[Tatsuki Makino]

Your poudriere.conf is written as PARALLEL_JOBS=4.
Combining this with writing MAKE_JOBS_NUMBER:=4 in
/usr/local/etc/poudriere.d/*make.conf, load average reaches 16.
If you are concerned about that load average reaching 16, you need to
adjust PARALLEL_JOBS and MAKE_JOBS_NUMBER.
If it only rise up to about 4, problem will remain somewhere.

There are some parts of bsd.port.mk that are not supposed to use -j, so
using .MAKE.JOBS will make things go wrong.
Some ports have problems with parallel build. (e.g. devel/doxygen has
MAKE_JOBS_UNSAFE=yes) I think .MAKE.JOBS will not follow it.
If slow port builds (e.g. cmake, llvm, qt5-webkit, texlive-texmf or
etc.) hinder others, load average will temporarily drop.