An error of -1 from parse_mount() indicates that the specification

was invalid. Don't trigger a mount failure (which by default means
a panic), but instead just move on to the next directive in the
configuration. This typically has us ask for the root mount.

PR:		163245

sys/kern/vfs_mountroot.c

@@ -791,6 +791,11 @@ vfs_mountroot_parse(struct sbuf *sb, struct mount *mpdevfs)
 			break;
 		default:
 			error = parse_mount(&conf);
+			if (error == -1) {
+				printf("mountroot: invalid file system "
+				    "specification.\n");
+				error = 0;
+			}
 			break;
 		}
 		if (error < 0)