Extend initial db delayed connect time (#257)

During periodic maintenance, I restarted the stack and noticed metadata
DB functions were off. It seemed the Postgres container was taking
longer than before to start.

This PR increases the hardcoded delay Cadence waits before making the
initial database connection.

Looking for a more proper way to do this with retries or through Docker
Compose. Until then, this should fix the stack.

cadence/server/db_postgres.go

@@ -20,7 +20,8 @@ var dbp *sql.DB
 
 func postgresInit() (err error) {
 	// We wait a bit to give some leeway for Postgres to finish startup.
-	time.Sleep(2 * time.Second)
+	// Obligatory: There's probably a better way to do this.
+	time.Sleep(5 * time.Second)
 	dsn := fmt.Sprintf("host='%s' port='%s' user='%s' password='%s' sslmode='%s'",
 		c.PostgresAddress, c.PostgresPort, c.PostgresUser, c.PostgresPassword, c.PostgresSSL)
 	dbp, err = sql.Open("postgres", dsn)