Adapt build node code to work with enabled SELinux

[anfimovdm]

When we try to build something with enabled SELinux we get the following error:

DEBUG util.py:459:  groupadd: /var/lib/mock/b3ea6a75030850a0899dec09154bac44f0e3ab2222e80262060d080b9a7ec1b0.0/root//etc/group.16137: Permission denied
DEBUG util.py:459:  groupadd: cannot lock /var/lib/mock/b3ea6a75030850a0899dec09154bac44f0e3ab2222e80262060d080b9a7ec1b0.0/root//etc/group; try again later.

However, some other errors might pop up too, we should check it and adapt our code to work with enabled SELinux