LU-313 re-enable lfsck test to run by default

Due to bug 13698, the lfsck part of the lfsck.sh test script was
disabled by default.   After the fixes in LU-113 were landed, lfsck
should work again.  Remove LFSCK_SKIP checks so lfsck.sh actually runs
lfsck instead of silently skipping it unless LFSCK_SKIP=no is set.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Idf7f0606c3937b0311db998032d58475076ab1a8
Reviewed-on: http://review.whamcloud.com/552
Tested-by: Hudson
Reviewed-by: Yu Jian <yujian@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Chris Gearing <chris@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>