ocfs2/cluster: move locking into attribute store methods

The test and separate set bit scheme was racy to start with, so move to do
a test_and_set_bit after doing the earlier error checks inside the actual
store methods.  Also remove the locking for the local attribute which
already has a different scheme to synchronize.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>