HBASE-19886 Display maintenance mode in shell, web UI

hbase-server/src/main/jamon/org/apache/hadoop/hbase/tmpl/master/MasterStatusTmpl.jamon

@@ -162,6 +162,12 @@ AssignmentManager assignmentManager = master.getAssignmentManager();
           re-enabled from the hbase shell by running the command 'catalogjanitor_switch true'
           </div>
         </%if>
+        <%if master.isInMaintenanceMode() %>
+          <div class="alert alert-warning">
+          Your Master is in maintenance mode. This may be because of HBCK aborting while
+          running in repair mode. Please re-run HBCK in repair mode.
+          </div>
+        </%if>
         <%if !master.isBalancerOn() %>
           <div class="alert alert-warning">
             The Load Balancer is not enabled which will eventually cause performance degradation

hbase-shell/src/main/ruby/hbase/admin.rb

@@ -190,6 +190,13 @@ module Hbase
       @admin.isNormalizerEnabled()
     end
 
+    #----------------------------------------------------------------------------------------------
+    # Query the current state of master in maintenance mode.
+    # Returns the state of maintenance mode (true is on).
+    def in_maintenance_mode?
+      @admin.isMasterInMaintenanceMode
+    end
+
     #----------------------------------------------------------------------------------------------
     # Request a scan of the catalog table (for garbage collection)
     # Returns an int signifying the number of entries cleaned

hbase-shell/src/main/ruby/shell.rb

@@ -327,6 +327,7 @@ Shell.load_command_group(
     normalize
     normalizer_switch
     normalizer_enabled
+    is_in_maintenance_mode
     close_region
     compact
     flush

hbase-shell/src/main/ruby/shell/commands/is_in_maintenance_mode.rb

@@ -0,0 +1,38 @@
+#
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+#
+
+module Shell
+  module Commands
+    class IsInMaintenanceMode < Command
+      def help
+        <<-EOF
+Is master in maintenance mode? For example:
+
+  hbase> is_in_maintenance_mode
+EOF
+      end
+
+      def command
+        state = admin.in_maintenance_mode?
+        formatter.row([state.to_s])
+        state
+      end
+    end
+  end
+end