fix for issue #1023

Better error for core size mismatch during activation/load

adding pyocf test for new error code

Signed-off-by: Piotr Debski <piotr.debski@intel.com>

inc/ocf_err.h

@@ -140,6 +140,9 @@ typedef enum {
 	/** Invalid operation for cache in standby state. */
 	OCF_ERR_CACHE_STANDBY,
 
+	/** Size of core volume doesn't match the size stored in cache metadata */
+	OCF_ERR_CORE_SIZE_MISMATCH,
+
 	/** Operation invalid with cache drive atatched in failover standby */
 	OCF_ERR_STANDBY_ATTACHED,