Improve TMS error handling (#89)

* hint to ECU-TEST logs

src/main/java/de/tracetronic/jenkins/plugins/ecutest/test/client/AbstractTMSClient.java

@@ -121,7 +121,7 @@ public Boolean call() throws IOException {
                 }
             } catch (final ETComException e) {
                 logger.logError("The test management module is not available in running ECU-TEST instance! "
-                    + "Enable it by setting the feature flag 'TEST-MANAGEMENT-SERVICE'.");
+                    + "Please check the ECU-TEST log files for more details.");
                 logger.logComException(e);
             }
             return isAvailable;