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: I005962a63341bb8585141dfe5dcff3ea79560b87
Signed-off-by: Moisés Guimarães de Medeiros <moguimar@redhat.com>