devel/uatraits: unbreak with boost 1.67

checking for boost_python... boost_python
checking boost/python.hpp usability... yes
checking boost/python.hpp presence... yes
checking for boost/python.hpp... yes
checking linkage with boost::python... no
[...]
configure: error: boost python isn't installed for python binding

PR: 227427
Reported by: antoine (via exp-run)