linting cleanup in cbsbuild.py
linting cleanup in cbsbuild.py

F821 undefined name 'exception'

converted to importing directly the ModuleNotAvailable and RpmModuleNotAvailable

Change-Id: I5687a70a1b289ad57b7bdd821ac4e4e74f80d429

redhat-openstack/rdopkg,openstack-packages/rdopkg,redhat-openstack/rdopkg,openstack-packages/rdopkg