apibuild: Fix indentation not multiple of 4
    
    PEP8 recommends that the number of spaces used for indentation of
    Python code to be a multiple of four [1] [2].
    
    1: https://lintlyci.github.io/Flake8Rules/rules/E111.html
    2: https://lintlyci.github.io/Flake8Rules/rules/E114.html
    
    Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
    Signed-off-by: Radostin Stoyanov <rstoyanov1@gmail.com>