uniquefiles.mk: Let ports override directories

[0mp]

Summary

This patch makes it possible to override directory manually names when
USES=uniquefiles:dirs is used. Some ports like Ansible have to override
values of ETCDIR and DATADIR in order to preserve the defaults and POLA.
Currently, Ansible ports override ETCDIR and DATADIR after including
bsd.port.mk, which feels like a hack.

[0mp]

Idea: Alternatively, maybe we can use ?= instead of = to assign those *DIR variables so that uniquefile.mk does not assign values if the port already did that.

[0mp]

Ping.

[0mp]

sysutils/ansible/Makefile is still using that ugly workaround:

.include <bsd.port.mk>

# Make sure that we override the unique DATADIR and ETCDIR set
# by the implicit USES=uniquefiles.
DATADIR=	${ANSIBLE_DATADIR}
ETCDIR=		${ANSIBLE_ETCDIR}

Let me know if I can land it.

[mat]

I'd rather we used ?= here.

Also, ansible ahould probably not be using USE_PYTHON=concurrent

[mat]

In D30315#1225899, @mat wrote:

Also, ansible ahould probably not be using USE_PYTHON=concurrent

And I know I am the one who added it, but at the time, we did produce two packages for ansible, one for python 2 and one for python 3.

As we don't produce python 2 ports any more, concurrent should probably be removed from ports like ansible.