anaconda is unable to decode config drive from base64

[Maryna Savchenko]

During the anaconda deployment, Ironic encodes the config drive to base 64 and writes the encoded string to the kickstart file. When the node boots and Anaconda starts the server installation, it can not decode it.
The reason is how Python's base 64 encoding works. Its format is b'encodedstring'.
Having 'b' at the beginning makes it impossible for Anaconda to decode it at a later stage.

To reproduce you need to have data on the metadata service:
* deploy node using Anaconda:
   - set the driver
   - create image
   - create a kickstart file with {{ ks_options.config_drive }} and assign it to the server or image
* Open the console and check anaconda logs in /var/anaconda during the installation