For warmup/rampup, only consider healthy backends

For healthy == IGNORE, we return before the call to shard_next(), so
at this point we do want to consider health state - and it makes
absolutely no sense to give up a healthy backend in favor of an un-
healthy one anyway.

Fixes #2823

bin/varnishtest/tests/d00023.vtc

@@ -13,6 +13,9 @@ server s3 {
 	rxreq
 	expect req.http.healthy == "true"
 	txresp -body "xiuFi3Pe"
+	rxreq
+	expect req.http.healthy == "true"
+	txresp -body "xiuFi3Pe"
 } -start
 
 varnish v1 -vcl+backend {
@@ -29,8 +32,16 @@ varnish v1 -vcl+backend {
 	}
 
 	sub vcl_recv {
-		set req.backend_hint = vd.backend(by=KEY,
-		    key=1756955383);
+		if (req.url == "/warmup") {
+			# key for which the order is s3->s1->s2
+			# we do not want to hit s1/s2 because they are down
+			set req.backend_hint = vd.backend(by=KEY,
+			    key=192192123, warmup=1.0);
+		} else {
+			# key for which the order is s1->s2->s3
+			set req.backend_hint = vd.backend(by=KEY,
+			    key=1756955383);
+		}
 		set req.http.healthy = std.healthy(req.backend_hint);
 		return(pass);
 	}
@@ -50,4 +61,7 @@ client c1 {
 	txreq
 	rxresp
 	expect resp.body == "xiuFi3Pe"
+	txreq -url "/warmup"
+	rxresp
+	expect resp.body == "xiuFi3Pe"
 } -run

lib/libvmod_directors/shard_dir.c

@@ -401,7 +401,7 @@ sharddir_pick_be(VRT_CTX, struct sharddir *shardd,
 
 	/* short path for cases we dont want ramup/warmup or can't */
 	if (alt > 0 || healthy == IGNORE || (!rampup && warmup == 0) ||
-	    shard_next(&state, 0, 0) == -1)
+	    shard_next(&state, 0, 1) == -1)
 		goto ok;
 
 	assert(alt == 0);