LU-10070 test: llapi_layout_test enhancements

LU-10070 test: llapi_layout_test enhancements

This patch improves the interactive behavior of
llapi_layout_test, by adding the ability to specify a
run list, rather than just a skip list.

Test-Parameters: trivial
Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: I2ec9de94c228f309c157a3d4e75615ab8581330a
Reviewed-on: https://review.whamcloud.com/33779
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Wei Liu <sarah@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>