Fix undertow-worker-thread-pool-scenario didn't lock Spring boot version (#399)

Author: nisiyong

test/plugin/scenarios/undertow-worker-thread-pool-scenario/configuration.yml

@@ -18,3 +18,5 @@ type: jvm
 entryService: http://localhost:8080/undertow-worker-thread-pool-scenario/case/undertow-worker-thread-pool-scenario
 healthCheck: http://localhost:8080/undertow-worker-thread-pool-scenario/case/healthCheck
 startScript: ./bin/startup.sh
+environment:
+  - SW_METER_REPORT_INTERVAL=1

test/plugin/scenarios/undertow-worker-thread-pool-scenario/pom.xml

@@ -79,6 +79,7 @@
             <plugin>
                 <groupId>org.springframework.boot</groupId>
                 <artifactId>spring-boot-maven-plugin</artifactId>
+                <version>${spring-boot-version}</version>
                 <executions>
                     <execution>
                         <goals>