prometheus: Add detailed metrics

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

test/shell/prometheus-3.sh

@@ -1,7 +1,5 @@
 #!/bin/bash -e
 
-exit 0	# FIXME: disabled until intermittent failures can be resolved
-
 # run a graph, with prometheus support
 timeout --kill-after=30s 25s ./mgmt run --tmp-prefix --no-pgp --prometheus --yaml prometheus-3.yaml &
 pid=$!