recipetool: create: hide missing npm error when called from devtool

recipetool: create: hide missing npm error when called from devtool

If devtool is called with a URL to a source repository containing a
node.js module, we don't know that until recipetool has fetched it, and
due to the structure of the code we have to exit with a special code in
order to let devtool know it needs to build nodejs-native. We also want
to suppress the error message that recipetool would normally print under
these circumstances; there is already a mechanism for this but it wasn't
operative in the case where we're pointed to a source repository rather
than an npm:// URL, so create some plumbing so that we know to hide the
message.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>