show-queue cannot be starved for admins

When admin executes the show-queue command a new thread will be
created to make sure that the commmand is always executed even if
the thread pool is exhausted.

Bug: issue 570

gerrit-sshd/src/main/java/com/google/gerrit/sshd/AdminHighPriorityCommand.java

@@ -0,0 +1,31 @@
+// Copyright (C) 2009 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package com.google.gerrit.sshd;
+
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+/**
+ * Annotation tagged on a concrete Command that requires
+ * high priority thread creation whenever called by administrators users.
+ * <p>
+ */
+@Target( {ElementType.TYPE})
+@Retention(RUNTIME)
+public @interface AdminHighPriorityCommand {
+}