Fix userland resource leaks

Coverity caught these. With the exception of the file descriptor leak in
tests/zfs-tests/cmd/draid.c, they are all memory leaks.

Also, there is a piece of dead code in zfs_get_enclosure_sysfs_path().
We delete it as cleanup.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13921

tests/zfs-tests/cmd/btree_test.c

@@ -233,13 +233,13 @@ drain_tree(zfs_btree_t *bt, char *why)
 		void *ret;
 
 		u_longlong_t randval = random();
-		node = malloc(sizeof (int_node_t));
 		if ((p = (uint64_t *)zfs_btree_find(bt, &randval, &bt_idx)) !=
 		    NULL) {
 			continue;
 		}
 		zfs_btree_add_idx(bt, &randval, &bt_idx);
 
+		node = malloc(sizeof (int_node_t));
 		node->data = randval;
 		if ((ret = avl_find(&avl, node, &avl_idx)) != NULL) {
 			snprintf(why, BUFSIZE, "Found in avl: %llu\n", randval);

tests/zfs-tests/cmd/draid.c

@@ -849,6 +849,7 @@ restart:
 			if (rc < 0) {
 				printf("Unable to read /dev/urandom: %s\n:",
 				    strerror(errno));
+				close(fd);
 				return (1);
 			}
 			bytes_read += rc;