Hard dependency on keyring package

[leamas]

Invoking ddupdate without the keyring package available fails since the logic tries to load the auth_keyring plugin unconditionally. This works not that well in servers, since unlocking the keyring always needs manual intervention.

This could be fixed downstream by moving the auth-keyring to a separate package not necessarily installed. However, best would be if the hard dependency introduced when handling #71 could be removed, and things works as expected even if the keyring package is not available.

Possible route: new global exception "Plugin unavailable"?