LU-9335 pfl: calculate PFL file LOVEA correctly

LU-9335 pfl: calculate PFL file LOVEA correctly

PFL file could contain uninstantiated component, so it could still
keeps the specified -1 stripe count,
lov_mds_md_size()/lov_user_md_size() should heed this case,
otherwise its LOVEA size could be errneous big.

Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: Ied4bf4531f0b0ac9fdefc9efef3c97ae5ae449f4
Reviewed-on: https://review.whamcloud.com/26597
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>