Vinyl meta via xlog format

We will write all vinyl metadata in xlog file format. Each run has its
own xlog with one transaction. First xrow should contain an run creation
request, all others - page creation requests.

src/box/schema.h

@@ -59,6 +59,10 @@ enum {
 	BOX_VPRIV_ID = 313,
 	/** Space id of _cluster. */
 	BOX_CLUSTER_ID = 320,
+	/** Space id of _vinyl_space. */
+	BOX_VINYL_RUN_ID = 328,
+	/** Space id of _vinyl_page. */
+	BOX_VINYL_PAGE_ID = 326,
 	/** End of the reserved range of system spaces. */
 	BOX_SYSTEM_ID_MAX = 511,
 	BOX_ID_NIL = 2147483647