dist/tools/flake8: use "python -m flake8", handle missing flake8
dist/tools/flake8: use "python -m flake8", handle missing flake8

kbumsik/RIOT,jasonatran/RIOT,rfuentess/RIOT,BytesGalore/RIOT,toonst/RIOT,RIOT-OS/RIOT,basilfx/RIOT,josephnoir/RIOT,gebart/RIOT,basilfx/RIOT,josephnoir/RIOT,authmillenon/RIOT,miri64/RIOT,smlng/RIOT,biboc/RIOT,OlegHahm/RIOT,authmillenon/RIOT,rfuentess/RIOT,x3ro/RIOT,gebart/RIOT,ant9000/RIOT,mfrey/RIOT,kbumsik/RIOT,rfuentess/RIOT,OlegHahm/RIOT,aeneby/RIOT,yogo1212/RIOT,miri64/RIOT,kaspar030/RIOT,gebart/RIOT,A-Paul/RIOT,avmelnikoff/RIOT,smlng/RIOT,cladmi/RIOT,lazytech-org/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,OlegHahm/RIOT,gebart/RIOT,OTAkeys/RIOT,rfuentess/RIOT,ant9000/RIOT,OTAkeys/RIOT,cladmi/RIOT,kYc0o/RIOT,OTAkeys/RIOT,avmelnikoff/RIOT,gebart/RIOT,toonst/RIOT,yogo1212/RIOT,avmelnikoff/RIOT,authmillenon/RIOT,kbumsik/RIOT,x3ro/RIOT,jasonatran/RIOT,BytesGalore/RIOT,toonst/RIOT,mtausig/RIOT,cladmi/RIOT,OTAkeys/RIOT,yogo1212/RIOT,neiljay/RIOT,josephnoir/RIOT,basilfx/RIOT,smlng/RIOT,aeneby/RIOT,mfrey/RIOT,miri64/RIOT,neiljay/RIOT,authmillenon/RIOT,kaspar030/RIOT,kYc0o/RIOT,rfuentess/RIOT,A-Paul/RIOT,mtausig/RIOT,josephnoir/RIOT,cladmi/RIOT,kYc0o/RIOT,cladmi/RIOT,BytesGalore/RIOT,aeneby/RIOT,neiljay/RIOT,biboc/RIOT,RIOT-OS/RIOT,x3ro/RIOT,jasonatran/RIOT,toonst/RIOT,ant9000/RIOT,neiljay/RIOT,kaspar030/RIOT,A-Paul/RIOT,avmelnikoff/RIOT,BytesGalore/RIOT,josephnoir/RIOT,kaspar030/RIOT,neiljay/RIOT,aeneby/RIOT,yogo1212/RIOT,yogo1212/RIOT,avmelnikoff/RIOT,kbumsik/RIOT,toonst/RIOT,OTAkeys/RIOT,ant9000/RIOT,A-Paul/RIOT,miri64/RIOT,mfrey/RIOT,biboc/RIOT,x3ro/RIOT,basilfx/RIOT,jasonatran/RIOT,lazytech-org/RIOT,ant9000/RIOT,aeneby/RIOT,kYc0o/RIOT,smlng/RIOT,A-Paul/RIOT,miri64/RIOT,lazytech-org/RIOT,biboc/RIOT,smlng/RIOT,OlegHahm/RIOT,kbumsik/RIOT,mfrey/RIOT,OlegHahm/RIOT,lazytech-org/RIOT,mtausig/RIOT,basilfx/RIOT,lazytech-org/RIOT,biboc/RIOT,mtausig/RIOT,kYc0o/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,authmillenon/RIOT,yogo1212/RIOT,mtausig/RIOT,x3ro/RIOT,authmillenon/RIOT,BytesGalore/RIOT,mfrey/RIOT