Added wrapper functions to update Schema's se_private_data from
ndbcluster.

Changes:
 ndb_dd_schema.h
 - Added this new header that has auxiliary functions that help in
   writing into the Schema object and extracting information from it.
 - Added functions to read and write the counter and nodeid values
   into Schema's se_private_data field.

 sql/ndb_dd_client.h
 - Updated the mdl_lock_schema() method to make it lock the Schema lock
   exclusively for updation if required.
 - Added a new function update_schema_version() that sets the version
   information of a Schema in the Schema object's se_private_data.

 sql/ndb_dd.h
 - Added a new function ndb_dd_update_schema_version(), a wrapper to
   the function update_schema_version() mentioned above.

Change-Id: I8204524018531ba2971c977a8d8d4e3962c29b7f