LU-11505 tests: customise run_*() functions

LU-11505 tests: customise run_*() functions

For PFL testing we need the ability to run
parallel-scale tests with composite files.
Patch adds the subtests' specific variables *_STRIPEPARAMS
which allow to set any specified striping/composite layout
for test directory.

Test-Parameters: trivial testlist=parallel-scale,parallel-scale-nfsv3
Signed-off-by: Elena Gryaznova <elena.gryaznova@hpe.com>
Cray-bug-id: LUS-5936
Reviewed-by: Alexander Boyko <c17825@cray.com>
Reviewed-by: Vladimir Saveliev <c17830@cray.com>
Change-Id: I767fa17523f5c40d50260892901dc947a1da8a24
Reviewed-on: https://review.whamcloud.com/33352
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>