There was no check for DATA/INDEX DIRECTORY for subpartitions

Added the same check as for partitions.

mysql-test/r/partition_error.result:
  Bug#42954: SQL MODE 'NO_DIR_IN_CREATE' does not work with subpartitions
  
  Updated results
mysql-test/t/partition_error.test:
  Bug#42954: SQL MODE 'NO_DIR_IN_CREATE' does not work with subpartitions
  
  Added tests
sql/partition_info.cc:
  Bug#42954: SQL MODE 'NO_DIR_IN_CREATE' does not work with subpartitions
  
  moved the check for DATA/INDEX DIRECTORY into a function
  and used it for both partitions as well as subpartitions.
  (Was not checked at all for subpartitions before)