Teach slapproxy to handle non-ascii instance parameters
Several fixes to make slapproxy accept creating instances with non-ascii parameters. My use-case it to instantiate gitlab with ICP, e.g. this way:
ICP = 沪ICP备14008524号kirr/gitlab-ce@1e11409c
kirr/slapos@66919597
/cc @rafael, @alain.takoudjou, @kazuhiko, @jerome, @arnau