Add a functionnality for Lustre to choose specific OSTs or all available OSTs as starting OST for testfile in POSIX mode with separate files

Add a functionnality for Lustre to choose specific OSTs or all available OSTs as starting OST for testfile in POSIX mode with separate files.

The main need for this functionnality is the possibility to bench all available OST in the Lustre file system

Changes:
- Add in configure file the test for LustreAPI
- Add an option for Lustre "lustreUseAllOsts" which activate the functionnality and give the choice of the OST used
- Add two functions in utilities.c : 
   * nodesete : read the OST list
   * get_active_ost_list : retrieve all available OSTs in the Lustre file system from the path of the testfiles
- Add the necessary lines in the user guide