apibuild: Fix indentation not multiple of 4

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>