MRP-1362 tests: Lustre Sanity test_101b hangs for large OSTCOUNTs

	sanity.sh test_101b hangs during Lustre sanity test. This
	is happening especially in cases where the $OSTCOUNT is
	greater than 100.

	Due to OSTCOUNT of more than 100, the ITERATION parameter
	results in '0', which causes the 'reads' utility to run
	in infinite 'for' loop. Thus resulting in a hang on such
       	setups.

	This change would make necessary changes in FILE_LENGTH in
	test_101b and its related routines(setup_101bc, ra_check)
	so that, the test won't hang and would proceed rightly.

Author: Parinay Kondekar <Parinay_Kondekar@xyratex.com>
Change-Id: Ida4b54f5129c9577dbb966289d7d18aec7071f0c