Cleanup collectors (#826)

Fix up `replication` and `process_idle` Update input params to match
the rest of the collectors.

Signed-off-by: SuperQ <superq@gmail.com>

collector/pg_replication.go

@@ -15,7 +15,6 @@ package collector
 
 import (
 	"context"
-	"database/sql"
 
 	"github.com/prometheus/client_golang/prometheus"
 )
@@ -64,7 +63,8 @@ var (
 	END as is_replica`
 )
 
-func (c *PGReplicationCollector) Update(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error {
+func (c *PGReplicationCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
+	db := instance.getDB()
 	row := db.QueryRowContext(ctx,
 		pgReplicationQuery,
 	)