[v6r8] make pylint happy + fixes

FIX: make pylint happy
FIX: Properly check if the pilot proxy has VOMS before adding it to the payload when updating it
FIX: Align properly days with MySQL bucketing. Closes #1219
FIX: Prevent duplicate key errors on writing VOMSProxies to DB. Closes #1228 
CHANGE: Moved log coloring to utilities so it can be used consistently across DIRAC