fix(dev-db/etcd): Handle missing ec2 user-data correctly.

Important notice to all using curl: by default a 404 is not an error!

I noticed that instances created without any user data were attempting
to connect to a *lot* of random IP addresses and failing. After
attempting the curl command c10n uses to fetch user data it would seem
we have lots of virtual machines using the following as a secret key:

    <?xml version="1.0" encoding="iso-8859-1"?>
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
             "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
     <head>
      <title>404 - Not Found</title>
     </head>
     <body>
      <h1>404 - Not Found</h1>
     </body>
    </html>

ᕙ(⇀‸↼‶)ᕗ

The --fail option is required for curl to behave responsibly.