Creates a new write closer that must be released
by the read consumer. This is necessary so that
while commiting the underlying writers in erasure
coding we need to make sure we reply success only if
we have committed to disk.
This in turn also fixes plethora of bugs related to
subsequent PutObject() races with namespace locking.
This patch also enables most of the tests, other than
ListObjects paging which has some issues still.
Fixes#1358, #1360
It is the bucket and volumes which needs to have this
value rather than the DiskInfo API itself. Eventually
this can be extended to show disk usage per
Buckets/Volumes whenever we have that functionality.
For now since buckets/volumes are thinly provisioned
this is the right approach.
