Scrub environment variable in tests

ExtUtils::Install now honours the PERL_INSTALL_QUIET env var
that silences output during pm_to_blib()
v0.037

          Scrub environment variable in tests
Scrub PERL_MB_OPT in tests too
Improve information about legacy local::lib
v0.038

          Scrub PERL_MB_OPT in tests too
Supply basename to *.PL files as its args
v0.039

          Supply basename to *.PL files as its args