Introduce zero-metadata command

Add function *zero_md* in *cas_lib* to handle
new command for zeroing metadata.

Signed-off-by: Slawomir Jankowski <slawomir.jankowski@intel.com>

casadm/cas_lib.h

@@ -267,6 +267,14 @@ int validate_str_stats_filters(const char* s);
 int validate_str_output_format(const char* s);
 int validate_str_metadata_mode(const char* s);
 
+/**
+ * @brief clear metadata
+ *
+ * @param[in] cache_device device to which zeroing cache's metadata applies
+ * @return 0 if succeed, 1 if failed
+ */
+int zero_md(const char *cache_device);
+
 /**
  * @brief calculate flush progress
  *