LU-1581 tests: restore CONF_SANITY_EXCEPT handling

LU-1581 tests: restore CONF_SANITY_EXCEPT handling

Commit 6a6561972406043efe41ae43b64fd278f360a4b9 removed the check in
conf-sanity.sh for a global test exception list.  This prevents
skipping tests from conf-sanity.sh when it is being run as part of a
larger set of tests, such as acceptance-small.sh.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I822cf5e9f873710c35321a88c94e576f15500c1e
Reviewed-on: http://review.whamcloud.com/4138
Tested-by: Hudson
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Wei Liu <wei3.liu@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>