minor fix

Author: xiancao

imagetool/src/test/java/com/oracle/weblogic/imagetool/integration/BaseTest.java

@@ -276,7 +276,8 @@ private static void pullDockerImage(String repoServer, String username, String p
         // verify the docker image is pulled
         ExecResult result = ExecCommand.exec("docker images | grep " + imagename  + " | grep " +
                 imagetag + "| wc -l");
-        if(Integer.parseInt(result.stdout().trim()) != 1) {
+        String resultString = result.stdout();
+        if(Integer.parseInt(resultString.trim()) != 1) {
             throw new Exception("docker image " + imagename + ":" + imagetag + " is not pulled as expected."
                     + " Expected 1 image, found " + resultString);
         }