resources: Update state checks

The mgmt graph depends on state tracking to eliminate redundant pokes.
With the Watch loop now able to produce events quickly, it should no
longer play a part in determining the vertex state. This simplifies the
resource API as well!

test/shell/t5b.sh

@@ -0,0 +1,7 @@
+#!/bin/bash -e
+
+# should take slightly more than 35s, but fail if we take 45s)
+timeout --kill-after=45s 40s ./mgmt run --yaml t5.yaml --converged-timeout=5 --no-watch --tmp-prefix &
+pid=$!
+wait $pid	# get exit status
+exit $?