JENKINS-49278 Get process list within containers by explicitly specifying ps output.

Author: hendrikhalkow

src/main/java/org/jenkinsci/plugins/docker/workflow/client/DockerClient.java

@@ -135,7 +135,7 @@ public String run(@Nonnull EnvVars launchEnv, @Nonnull String image, @CheckForNu
     }
 
     public List<String> listProcess(@Nonnull EnvVars launchEnv, @Nonnull String containerId) throws IOException, InterruptedException {
-        LaunchResult result = launch(launchEnv, false, "top", containerId);
+        LaunchResult result = launch(launchEnv, false, "top", containerId, "-eo", "pid,comm");
         if (result.getStatus() != 0) {
             throw new IOException(String.format("Failed to run top '%s'. Error: %s", containerId, result.getErr()));
         }
@@ -146,12 +146,10 @@ public List<String> listProcess(@Nonnull EnvVars launchEnv, @Nonnull String cont
             in.readLine(); // ps header
             while ((line = in.readLine()) != null) {
                 final StringTokenizer stringTokenizer = new StringTokenizer(line, " ");
-                if (stringTokenizer.countTokens() < 4) {
+                if (stringTokenizer.countTokens() < 2) {
                     throw new IOException("Unexpected `docker top` output : "+line);
                 }
                 stringTokenizer.nextToken(); // PID
-                stringTokenizer.nextToken(); // USER
-                stringTokenizer.nextToken(); // TIME
                 processes.add(stringTokenizer.nextToken()); // COMMAND
             }
         }