Fix tests and add an env var.

Hi @jquelin,

this commit fixes the tests due to POE giving warnings, and the encoding stuff of Dist-Zilla - see https://github.com/rjbs/Dist-Zilla/issues/270 and also adds an environment option for CPAN2Pkg to skip running "cpanp x ..." on every single time, which is time consuming (even on my fast Core i3) and annoying.

Regards,

-- @shlomif