proxy: Update timestamp partition on slave changes

Each time slave partition changes (it is added or updated) the master
partition timestamp has to be recalculated.
2 jobs for fix/slapos-core-slave-timestamp in 0 seconds
Status Job ID Name Coverage
  External
failed SlapOS.Eggs.UnitTest-luke.Python2

01:03:10

failed SlapOS.Eggs.UnitTest-luke.Python3

00:35:24