forced masters should not respond to clients when they're not the master,
as this could mean some updates are not yet applied to the store

(cherry picked from commit 985e99494dd981d3d4dff44f84de47061b6c2913)

Conflicts:
	src/node/sync_backend.ml
clear any self master sets applied to the store after initial catchup at node start

    (cherry picked from commit d3e60f794f159aee7e4cb829a4e959dff944f22c)
fix test_expect_progress_fixed_master
Merge remote-tracking branch 'refs/remotes/origin/backport-forced-master' into origin-1.6

Conflicts:
	src/node/node_main.ml