Create missing directories required by the agent

[siegfriedweber]

The following directories should be created if they are missing:

• config
• data
• log
• package
• directory of the certificate file if the file does not exist
• directory of the key file if the file does not exist

The directories should be created with the default mask. The only security relevant file for now (!) is the private key file which is already created with proper access rights (see #235).

If a directory was created then an information should be logged. If the creation failed then an error should be logged but the process should not terminate because this does not necessarily pose a problem later.

The creation must be performed before the accessibility of the directories is checked (see #45).

As next steps, missing directories required by the services/operators could be created (see #271) and the ownership of the newly created directories and the existing ones should be adapted (see #269).