Only flush superblock at the end of cache attach

The purpose of this change is not to write superblock to the cache
drive untill all other sections are initilized on disk in attach()
path. Combined with superblock clearing at the erarlier stage of
attach(), this assures there are no residual mappings in the collision
section in case of power failure during attach with pre-existing
metadata.

This is implemented by removing ocf_metadata_flush_all_set_status() step
at the beginning of ocf_metadata_flush_all().
ocf_metadata_flush_all() is called, except for the attach() case described
above, in two cases:
1. at the end of cache load - potentially after cache recovery
2. during detaching cache drive in cache stop.

To make sure there are no regressions in the first case, an explicit
_ocf_mngt_attach_shutdown_status() is added to load pipeline before
ocf_metadata_flush_all(). The second case is always ran after cache
drive is attached, so dirty status bit must have already be written to
the disk.

Signed-off-by: Adam Rutkowski <adam.j.rutkowski@intel.com>

src/metadata/metadata.c

@@ -991,8 +991,6 @@ struct ocf_pipeline_properties ocf_metadata_flush_all_pipeline_props = {
 	.priv_size = sizeof(struct ocf_metadata_context),
 	.finish = ocf_metadata_flush_all_finish,
 	.steps = {
-		OCF_PL_STEP_ARG_INT(ocf_metadata_flush_all_set_status,
-				ocf_metadata_dirty_shutdown),
 		OCF_PL_STEP_FOREACH(ocf_metadata_flush_segment,
 				ocf_metadata_flush_all_args),
 		OCF_PL_STEP_FOREACH(ocf_metadata_calculate_crc,

src/mngt/ocf_mngt_cache.c

@@ -1737,6 +1737,7 @@ struct ocf_pipeline_properties _ocf_mngt_cache_load_pipeline_properties = {
 		OCF_PL_STEP(_ocf_mngt_load_add_cores),
 		OCF_PL_STEP(_ocf_mngt_load_metadata),
 		OCF_PL_STEP(_ocf_mngt_load_post_metadata_load),
+		OCF_PL_STEP(_ocf_mngt_attach_shutdown_status),
 		OCF_PL_STEP(_ocf_mngt_attach_flush_metadata),
 		OCF_PL_STEP(_ocf_mngt_attach_shutdown_status),
 		OCF_PL_STEP(_ocf_mngt_attach_post_init),