LU-9324 test: get layout parameters

LU-9324 test: get layout parameters

Add test framework functions get_layout_param()/parse_layout_param
to get plain/PFL file/dir layout parameters, so that the layout
parameters can be used later.

Test-Parameters: trivial testlist=sanity-pfl
Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Change-Id: I4f43a5b4d23e353660114b7ff299a97afc405a07
Reviewed-on: https://review.whamcloud.com/26578
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>