Fix wrong default value of `scheduler_filter_classes`

Default value of 'scheduler_filter_classes' configuration should be
'nova.cells.filters.all_filters'.

Change-Id: I942cf5ce4e69beafbc3cec497e16511bb87c4c79
Closes-Bug: #1385683
backport: juno
Merge "Fix wrong default value of `scheduler_filter_classes`"