The MAKE_JOBS_NUMBER was written to make.conf that get mounted over

ref/etc gets mounted on, many times with a null mount.  Each mount then
gets a copy of ref/etc2.  So the modifications to make.conf have to go
in etc2, not etc.
Generate category makefiles after ports creation / update

Poudriere requires the top level and category makefiles in the ports tree
to calculate dependencies.  The makefiles that dports has are not suitable
(they are dynamic) and they will also be removed in the near future.  As
such, poudriere needs to generate makefiles in the format it wants.  This
works because every port in the ports tree is considered valid -- and thus
should be tied into the build.