Reduce log output for price nodes

In case a price feed has an error, a stacktrace dumped in the logs
for each incoming getAllMarketPrice request. In detail, there is one
line of log stating that there is a getAllMarketPrice request, one
line of log stating that there is an error and around 150 lines of
stracktrace.
This fills up the logs quite fast, around 7.5G per day which is
unnecessary.
This commit only outputs the stacktrace in debug log configuration.

pricenode/src/main/java/bisq/price/spot/ExchangeRateService.java

@@ -84,7 +84,8 @@ private Map<String, Object> getMetadata(ExchangeRateProvider provider, Set<Excha
             timestamp = getTimestamp(provider, exchangeRates);
         } catch (Throwable t) {
             log.error(t.toString());
-            t.printStackTrace();
+            if (log.isDebugEnabled())
+                t.printStackTrace();
         }
 
         if (provider instanceof BitcoinAverage.Local) {