This is not used, not tested and causes SyntaxWarning on python 3.8:

    slapos/recipe/npm.py:128: SyntaxWarning: "is not" with a literal. Did you mean "!="?
      if npm_process.returncode is not 0:

This recipe alters a system perl ( or perl installed by another buildout
recipe ), which is not consistent with the independence of parts we are
trying to achieve in order to be able to cache and share parts.

SlapOS comonents now expose a `perl-CPAN-package` macro that should be
used for consistency. See slapos!341

/reviewed-on !4

Since slapos.libnetworkcache needs configuration, the user already
pulls it explicitely. Do not annoy those who don't use it.

In our case, it breaks offline builds with Python 2.6 when the
download-cache is prepared with Python 2.7: argparse missing.