env/linux-x86-stretch, dashboard: add swig, move linux-amd64 from jessie

Fixes golang/go#28857

Change-Id: Ifdd62dc8eac6ce52f9dc9ce8b3d2fcd92d4d1b26
Reviewed-on: https://go-review.googlesource.com/c/build/+/170282
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 02b1eca..c1425e6 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -1339,7 +1339,7 @@
 	})
 	addBuilder(BuildConfig{
 		Name:     "linux-amd64",
-		HostType: "host-linux-jessie",
+		HostType: "host-linux-stretch",
 		tryBot:   defaultTrySet(),
 		env: []string{
 			"GO_DISABLE_OUTBOUND_NETWORK=1",
diff --git a/env/linux-x86-stretch/Dockerfile b/env/linux-x86-stretch/Dockerfile
index 67e3440..50003f0 100644
--- a/env/linux-x86-stretch/Dockerfile
+++ b/env/linux-x86-stretch/Dockerfile
@@ -39,6 +39,7 @@
 	mercurial \
 	subversion \
 	iptables \
+	swig \
 	&& rm -rf /var/lib/apt/lists/*
 
 RUN mkdir -p /go1.4-amd64 \