Resolve "Create a script to implement account key rollover"

Closes #3

See merge request !8

To correctly fix it, we need to create a JWS function

use of key thumbprints

* Use more specific test module (we'll create new test modules for future tools)
* Create gitlab-ci job for Debian Jessie and Debian Jessie + backports

Apply Nonce update to acme_account_delete script too

Closes #4

See merge request !7

Nonce: use Nonce received in latest ACME server response if available

Closes #4

See merge request !6

Use of ACME Directory and automatic update agreement to terms of service

* Update main script to:
  * Use the ACME directory to retrieve correct URLs from the ACME servers
  * Be able to update account informations (contact information and agreed terms of service)
  * Read terms of service links from either the ACME directory or account informations
  * Automatically update terms of service agreement with latest changes (user have to stay informed about the updates himself)
  * Fix HTTP errors handling
* Update configuration to:
  *  Configure ACME directory instead of CAUrl
  *  Allow to specify contact informations (email and phone number ; beware that Let's Encrypt servers don't allow phones)
* Update tests to:
  * Correctly setup before running tests without using global variable
  * Correctly clean setup after running tests (correctly remove ACME account and close temporary files)
  * Update requirements to latest dnspython release (as release 1.15 has fixed the dns updates issue)
* Update account delete script (you can find it in /tests/) according to updates of the main script

See merge request !5

Latest release of dnspython have fixed the bug from 1.14.0 release.

Note: as boulder doesn't currently support phone informations, we can't test it.

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