Add missing dependencies for flake8

Make sure to explicitly declare those dependencies of flake8 that are provided already via LCG. This ensures that the relevant RPM packages get installed.

Also add a Find-module for functools32.

AE Build SUCCESS
Build logfiles are available at Jenkins [AE-MERGE-REQUEST-CC7 #41]

@akraszna, as discussed I would need quickly a new tag of atlasexternals with this.

mentioned in commit 2ca3bb74

merged

Here you go: https://gitlab.cern.ch/atlas/atlasexternals/tags/2.0.33

Thanks! athena!24715 (merged)