Bump bandit version

This patch bumps bandit allowed version to >=1.6.0,<1.7.0 in order to
avoid the errors detailed here https://github.com/PyCQA/bandit/pull/393



Change-Id: Ic61bffb3845a53df14765194482f6264417d0ac7
Signed-off-by: Moisés Guimarães de Medeiros <moguimar@redhat.com>