LU-9268 tests: check obj distribution for PFL striping

LU-9268 tests: check obj distribution for PFL striping

Add test to sanity-pfl to verfy that new components are
distributed evenly among OSTs for composite files.

Test-Parameters: trivial osscount=3 ostcount=4 testlist=sanity-pfl
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Signed-off-by: James Nunez <james.a.nunez@intel.com>
Change-Id: I0335fd376f6008529885236faad19a29eb01d5ba
Reviewed-on: https://review.whamcloud.com/26863
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Reviewed-by: Patrick Farrell <paf@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>