- bug: we were dumping the received secrets locally to disk *before*
  setting the received property for the active secret, and therefore the
  'active_secret' was always marked as null.
- refactor common code into an utility method.

- Resolves: #7412

From:
[refactor] removing getters and setters from couch.py
_couch_url was a private variable with getter and setter doing the same
as a public variable. It is accessed all over the code, so being private
with getters and setters didnt make sense. This commit fixes the tests
to also follow this style from now on.

Previous to this modification, the initialization of the sync decrypter pool
could happen concurrently with other database operations. That could cause the
pool to hang because it could be waiting for something that was mistakenly
deleted because of the wrong order of database operations.

This commit implements a standard which we already use in leap.keymanager and
leap.mail which makes some methods wait for the initialization operation
before they are actually called.

Closes: #7386

SoledadCrypto had Soledad as parameter to be able to use
SoledadSecrets. SoledadSecrets had SoledadCrypto as parameter to use
*crypt_sym. This commit removes this circular dependency passing
directly the secret that SoledadCrypto cares about to the constructor
and removing the *crypt_sym methods from SoledadCrypto.

- Resolves: #7338