LU-10673 tests: sanity test_56a fixes

LU-10673 tests: sanity test_56a fixes

The $filenum is not equal to $found if stripe_count
more then 1.
The $filenum is not equal to $found if stripe_index
is not default.
Patch fixes the following:
 We will counted files twice with dual striped
 file as they will have objects on both stripes.
 Remove dir's stripe-offset from stripes-offset's sum of
 test dirs/files which get by getstripe -ir.

Author: Alyona Romanenko <alyona.romanenko@seagate.com>

Signed-off-by: Alyona Romanenko <alyona.romanenko@seagate.com>
Signed-off-by: Elena Gryaznova <c17455@cray.com>
Test-Parameters: trivial testlist=sanity envdefinitions=ONLY=56a
Cray-bug-id: MRP-2738
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Reviewed-by: Parinay Kondekar <parinay.kondekar@seagate.com>
Change-Id: I911bf8b40b7688b4341f48409d9c5b57386cfe3d
Reviewed-on: https://review.whamcloud.com/31326
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>