cleanup: execute test_if_create_new_users as part of grant_stage0

There is identical logic for all grant functions. If a grant grants to
non existant users they are created if the SQL mode is not
NO_AUTO_CREATE_USER *and* the user granting has rights to create users.

This check is done via test_if_create_new_users. Refactor all code such
that this check is only done in one (or three places for-now till more
refactoring happens).

sql/sql_acl.h

@@ -348,6 +348,7 @@ class Sql_cmd_grant: public Sql_cmd
 {
 protected:
   enum_sql_command m_command;
+  bool m_create_new_users;
   List<LEX_USER> m_resolved_users;
 #ifndef NO_EMBEDDED_ACCESS_CHECKS
   void warn_hostname_requires_resolving(THD *thd, List<LEX_USER> &list);
@@ -356,7 +357,7 @@ class Sql_cmd_grant: public Sql_cmd
 #endif
 public:
   Sql_cmd_grant(enum_sql_command command)
-   :m_command(command)
+   :m_command(command), m_create_new_users(false)
   { }
   bool is_revoke() const { return m_command == SQLCOM_REVOKE; }
   enum_sql_command sql_command_code() const { return m_command; }
@@ -394,8 +395,10 @@ class Sql_cmd_grant_object: public Sql_cmd_grant
 class Sql_cmd_grant_table: public Sql_cmd_grant_object
 {
 #ifndef NO_EMBEDDED_ACCESS_CHECKS
-  bool execute_table_mask(THD *thd);
-  bool execute_exact_table(THD *thd, TABLE_LIST *table);
+  bool execute_grant_database_or_global(THD *thd);
+  bool execute_grant_global(THD *thd);
+  bool execute_grant_database(THD *thd);
+  bool execute_grant_table(THD *thd, TABLE_LIST *table);
 #endif
 public:
   Sql_cmd_grant_table(enum_sql_command command, Grant_privilege &grant)