YARN-5793. Trim configuration values in DockerLinuxContainerRuntime (Contributed by Tianyin Xu via Daniel Templeton)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/containermanager/linux/runtime/DockerLinuxContainerRuntime.java

@@ -219,9 +219,10 @@ public class DockerLinuxContainerRuntime implements LinuxContainerRuntime {
     dockerClient = new DockerClient(conf);
     allowedNetworks.clear();
     allowedNetworks.addAll(Arrays.asList(
-        conf.getStrings(YarnConfiguration.NM_DOCKER_ALLOWED_CONTAINER_NETWORKS,
+        conf.getTrimmedStrings(
+            YarnConfiguration.NM_DOCKER_ALLOWED_CONTAINER_NETWORKS,
             YarnConfiguration.DEFAULT_NM_DOCKER_ALLOWED_CONTAINER_NETWORKS)));
-    defaultNetwork = conf.get(
+    defaultNetwork = conf.getTrimmed(
         YarnConfiguration.NM_DOCKER_DEFAULT_CONTAINER_NETWORK,
         YarnConfiguration.DEFAULT_NM_DOCKER_DEFAULT_CONTAINER_NETWORK);
 
@@ -237,7 +238,7 @@ public class DockerLinuxContainerRuntime implements LinuxContainerRuntime {
       throw new ContainerExecutionException(message);
     }
 
-    privilegedContainersAcl = new AccessControlList(conf.get(
+    privilegedContainersAcl = new AccessControlList(conf.getTrimmed(
         YarnConfiguration.NM_DOCKER_PRIVILEGED_CONTAINERS_ACL,
         YarnConfiguration.DEFAULT_NM_DOCKER_PRIVILEGED_CONTAINERS_ACL));
   }
@@ -439,9 +440,10 @@ public class DockerLinuxContainerRuntime implements LinuxContainerRuntime {
         LOCALIZED_RESOURCES);
     @SuppressWarnings("unchecked")
     List<String> userLocalDirs = ctx.getExecutionAttribute(USER_LOCAL_DIRS);
-    Set<String> capabilities = new HashSet<>(Arrays.asList(conf.getStrings(
-        YarnConfiguration.NM_DOCKER_CONTAINER_CAPABILITIES,
-        YarnConfiguration.DEFAULT_NM_DOCKER_CONTAINER_CAPABILITIES)));
+    Set<String> capabilities = new HashSet<>(Arrays.asList(
+        conf.getTrimmedStrings(
+            YarnConfiguration.NM_DOCKER_CONTAINER_CAPABILITIES,
+            YarnConfiguration.DEFAULT_NM_DOCKER_CONTAINER_CAPABILITIES)));
 
     @SuppressWarnings("unchecked")
     DockerRunCommand runCommand = new DockerRunCommand(containerIdStr,