acme-dns: improve cURL error handling

[loganmzz]

Hello,

A very small change (at the moment, see below) in order to improve cURL error handling. cURL isn't a good HTTP client in regard of how to catch misc errors. This PR add common pattern around error handling with cURL:

• silent: Disable feedback output (just leaving useful information)
• show errors: Still display non-HTTP related messages on stderr (e.g. invalid certificates, unresolve names, etc.)
• temporary output: Body is sent to a temporary file for reuse later (and still read HTTP status from stdout)
• write output: Let's read HTTP status

Discussion about this PR is highly open, but some interesting point that need to be discussed:

• Provided cURL options are passed at last for possible override. Not sure it's desirable, but that let's open for tweaks.
• Modifications has been only applied for my direct needs and don't even look at other cURL invocation in the project. Should I check all cURL calls ?
• I don't really look at your coding conventions (except spacing) such as naming, comment, etc. Feel free to suggest udpate !