Existing passx enries resulted in a stacktrace because
the cp.get() call for the passx entries was missing.
Also added a delete_password function for ObfuscatedPasswordManager
to delete passx entries
If a python-keyring based backend is configured, but
python-keyring is not installed osc fails without giving
the user the opportunity to continue.
This introduces a new class method `create` for the AbstractCredentialsManager.
The CredentialsManagers for the backends that use a 3rd party software can
now check if the software is present in its own create method.
* new module credentials.py which contains classes
and methods to set and get passwords for different
backends:
- python-keyring
- gnomekeyring
- ConfigFile based storage
The new code should be backward compatible except a minor
change in add_section (pass and passx are not removed from
the config parser). This affects only callers that do not pass
a creds_mgr_descriptor.
On initial osc call or initial osc call on new API Url
the user now can decide where to store the password (based
on the backends available on his system)
