mt-backup

Add functionality to NDBFS to support new multithreaded backup
directory structure.

Example of current directory structure in backup path (backup
files present in BACKUP-<backupID> directory):

mysql@psangam-T460:~$ ls data2/BACKUP/
BACKUP-1  BACKUP-2
mysql@psangam-T460:~$ ls data2/BACKUP/BACKUP-1/
BACKUP-1-0.2.Data  BACKUP-1.2.ctl  BACKUP-1.2.log

Example of new directory structure for mt-backup (backup
subfolders in BACKUP-<backupID>, subfolders contain backup files):

mysql@psangam-T460:~$ ls data2/BACKUP/BACKUP-1/
BACKUP-1-PART-1-OF-4  BACKUP-1-PART-2-OF-4  BACKUP-1-PART-3-OF-4  BACKUP-1-PART-4-OF-4
mysql@psangam-T460:~$ ls data2/BACKUP/BACKUP-1/BACKUP-1-PART-1-OF-4/
BACKUP-1-0.2.Data  BACKUP-1.2.ctl  BACKUP-1.2.log
mysql@psangam-T460:~$ ls data2/BACKUP/BACKUP-1/BACKUP-1-PART-2-OF-4/
BACKUP-1-0.2.Data  BACKUP-1.2.ctl  BACKUP-1.2.log
mysql@psangam-T460:~$ ls data2/BACKUP/BACKUP-1/BACKUP-1-PART-3-OF-4/
BACKUP-1-0.2.Data  BACKUP-1.2.ctl  BACKUP-1.2.log
mysql@psangam-T460:~$ ls data2/BACKUP/BACKUP-1/BACKUP-1-PART-4-OF-4/
BACKUP-1-0.2.Data  BACKUP-1.2.ctl  BACKUP-1.2.log

NDBFS is now aware of the backup part in the file-open operation, as
well as the total number of backup parts. If a backup part ID is set
to 0, it creates files as per the old single-threaded backup directory
structure. If a non-zero part ID is set, it creates files as per the
mt-backup directory structure.