LU-8998 clio: Client side implementation for PFL

LU-8998 clio: Client side implementation for PFL

Make client layer support composite layout.

Plain layout will be stored in LOV layer as a composite layout
containing a single component.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: Ic3b85a4b10c66745e5c72ff02ea313baa0b12bb5
Reviewed-on: https://review.whamcloud.com/24850
Tested-by: Jenkins
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>