LU-1798 tests: add set_and_check to test-framework

Move the set_and_check() helper function from conf-sanity.sh into
test-framework.sh as set_conf_param_and_check() so that it can be
used in other test scripts.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I4ad3179decff55a0ec17a4c983e30941cf49cab0
Reviewed-on: http://review.whamcloud.com/4140
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Wei Liu <wei3.liu@intel.com>
Reviewed-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>