acme-dns-tiny: fixup registration process, we can log with account_url only after processing headers

Clean log of useless headers
For base64, remove only trailing '=' as defined in acme drafts

As this variable is used with _send_signed_request we have
to be sure to not overwrite it in the script.

Set try count to begin with 1 and do 10 tries.

Enable ACMEDirectory for new-reg part.

Enable use of dynamic terms-of-service url for the agreement part too ( fixes #1 ).

Enable a way to add contact information inside account registration (email and phone).
It allows the ACME server provider to contact you on terms of service modifications.

Fix HTTPError exception handling (use correct error from urllib.error instead of IOError).

This part use ACMEDirectory in requests to ACME server.
Next part will remove last remaining CAUrl code and enable dynamic agreement url.

This commit update configuration constraints to use ACMEDirectory instead of CAUrl.
Next part will use effectively this new configuration to do requests to ACME server.

logassert was added as requirements as the check have to look for log messages

The algorithm names match now the names used in dnssec-keygen and dnspython tools.

This check use the DNS server defined in DNS section (Host setting).

For each host, the script will :
1. push update to the DNS host
2. wait delay configured in seconds with parameter CheckChallengeDelay
3. ask the DNS host for TXT entries corresponding to the challenge
4. check if at least one entry corresponds to the key authorization
    * if there's one, let ask to the acme server to check themselves
    * if there's none:
        * wait 2 seconds and retry from step 3 (retry 10 times)
5. If after 10 retries nothing happend, stop with error

So, we have this behavior:
* if user knows its setup has no bottleneck and won't apply delay before checks,
   he sets CheckChallengeDelay to 0.
* if user knows there's some bottleneck for DNS update, it can set CheckChallengeDelay
   to a specific amount of seconds

In both case, the script will ensure it won't bother the ACME server with useless
operations.

configurable

Thanks to @rspeed for PR diafygi/acme-tiny#89

If the script was able to add a DNS record, it must remove it before end of
execution (even in case of errors).

Note: support of Python 2 was removed to simplify scripts and to be able
to manage correctly the default configuration if the INI file don't
contain some values (as DNS port, ACME url).

It currently works with dnsypython 1.11:
some error occured while creating TSIG keyring with 1.14 version.

The code was a little bit rearranged to have all helper functions at the top.

The way to write strings was also uniformised (use by default double quote,
and use simple quote when it's simpler)

As DNS update needs a lot of parameters, the code will now use a configuration
file in INI format.

fixed #58, apparently .reason isn't an attribute on HTTPError in python 2.6 even though it's documented as such