Resolve tox substitutions to absolute paths
Since tox-3.8.0 the substituted virtualenv-paths of tox
(like {envpython} or {envsitepackagesdir}) have become relative.
The documentation says nothing about this. Thus, these paths
should always be resolved as absolute.
https://github.com/tox-dev/tox/issues/1339
Fixes: https://pagure.io/freeipa/issue/7977
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>