LU-8998 docs: man pages for tools of PFL

LU-8998 docs: man pages for tools of PFL

Added new options to 'lfs find' and 'lfs getstripe' for composite
files. Moved "lfs setstripe/migrate" into separate man page, and
added new options for the operations to composite file.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I9cafde834be5c3d890bf04a3efb2ea973364596a
Reviewed-on: https://review.whamcloud.com/25741
Tested-by: Jenkins
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>