Bug#28785 thread-handling not displayed properly in SHOW VARIABLES

mysql-test/r/no-threads.result:
  Test that we are in the 'no-threads' thread_handling mode.
mysql-test/t/no-threads.test:
  Test that we are in the 'no-threads' thread_handling mode.
sql/mysqld.cc:
  Changes to make global_system_variables.thread_handling be zero based, instead of 1
  based.
sql/scheduler.h:
  Changed the enum to start at 0, to match the array elements in thread_handling_names
  in mysqld.cc

mysql-test/r/no-threads.result

@@ -4,3 +4,6 @@ select 1+1;
 select 1+2;
 1+2
 3
+SHOW GLOBAL VARIABLES LIKE 'thread_handling';
+Variable_name	Value
+thread_handling	no-threads

mysql-test/t/no-threads.test

@@ -3,3 +3,4 @@
 #
 select 1+1;
 select 1+2;
+SHOW GLOBAL VARIABLES LIKE 'thread_handling';

sql/mysqld.cc

@@ -7745,12 +7745,13 @@ mysqld_get_one_option(int optid,
     break;
   }
   case OPT_ONE_THREAD:
-    global_system_variables.thread_handling= 2;
+    global_system_variables.thread_handling=
+      SCHEDULER_ONE_THREAD_PER_CONNECTION;
     break;
   case OPT_THREAD_HANDLING:
   {
     global_system_variables.thread_handling=
-      find_type_or_exit(argument, &thread_handling_typelib, opt->name);
+      find_type_or_exit(argument, &thread_handling_typelib, opt->name)-1;
     break;
   }
   case OPT_FT_BOOLEAN_SYNTAX:

sql/scheduler.h

@@ -40,7 +40,7 @@ class scheduler_functions
 
 enum scheduler_types
 {
-  SCHEDULER_ONE_THREAD_PER_CONNECTION=1,
+  SCHEDULER_ONE_THREAD_PER_CONNECTION=0,
   SCHEDULER_NO_THREADS,
   SCHEDULER_POOL_OF_THREADS
 };