Add failing scan error test

This test demonstrates that when Bitcask's scan files operation fails,
a keydir object is created, not marked ready and left behind. Subsequent
open operations are unable to succeed because they try to wait for this
existing keydir to be ready when its data loads. But this will never
happen, so sadness ensues.
Fix scan error deadlock

If a file scan error happens during a Bitcask open operation, remember
to release the newly created keydir.  Before, that keydir was left
behind. Subsequent open operations would see it, see that it was not
ready yet and try to wait for it to load. But this would never happen,
alas.

If a scan error happens on opening a new directory, please release the
newly created keydir so other open operations have a chance to succeed.
Merge pull request #190 from basho/bugfix/scan-error-deadlock

Fix scan error deadlock

Reviewed-by: slfritchie