Don't bother retrying locking on read-only filesystem (RhBug:1502134)

upstream commit f25752a8cd6b161f3002dc7839242872ecb59547
--- ./lib/rpmlock.c.orig	2017-08-10 08:08:07.122108699 +0000
+++ ./lib/rpmlock.c	2017-12-05 12:02:26.248459858 +0000
@@ -30,7 +30,8 @@ static rpmlock rpmlock_new(const char *l
 	(void) umask(oldmask);
 
 	if (lock->fd == -1) {
-	    lock->fd = open(lock_path, O_RDONLY);
+	    if (errno != EROFS)
+		lock->fd = open(lock_path, O_RDONLY);
 	    if (lock->fd == -1) {
 		free(lock);
 		lock = NULL;