Update wsrep_sync_wait documentation as per MW-86

mysql-test/r/mysqld--help.result

@@ -942,8 +942,8 @@ The following options may be given as the first argument:
  --wsrep-sync-wait[=#] 
  Ensure "synchronous" read view before executing an
  operation of the type specified by bitmask: 1 -
- READ(includes SELECT, SHOW and BEGIN/START TRANSACTION);
- 2 - UPDATE and DELETE; 4 - INSERT and REPLACE
+ READ(includes SELECT and BEGIN/START TRANSACTION); 2 -
+ UPDATE and DELETE; 4 - INSERT and REPLACE; 8 - SHOW
 
 Variables (--variable-name=value)
 allow-suspicious-udfs FALSE

sql/sys_vars.cc

@@ -3897,8 +3897,8 @@ static Sys_var_mybool Sys_wsrep_causal_reads(
 static Sys_var_uint Sys_wsrep_sync_wait(
        "wsrep_sync_wait", "Ensure \"synchronous\" read view before executing "
        "an operation of the type specified by bitmask: 1 - READ(includes "
-       "SELECT, SHOW and BEGIN/START TRANSACTION); 2 - UPDATE and DELETE; 4 - "
-       "INSERT and REPLACE",
+       "SELECT and BEGIN/START TRANSACTION); 2 - UPDATE and DELETE; 4 - "
+       "INSERT and REPLACE; 8 - SHOW",
        SESSION_VAR(wsrep_sync_wait), CMD_LINE(OPT_ARG),
        VALID_RANGE(WSREP_SYNC_WAIT_NONE, WSREP_SYNC_WAIT_MAX),
        DEFAULT(WSREP_SYNC_WAIT_NONE), BLOCK_SIZE(1),