Move sslip.io-dns-server source code to a subdir

I'm going to create a simple HTTP/DNS server that has the same API as
[acme-dns](https://github.com/joohoi/acme-dns) but isn't so complicated,
and I want that code to be next to the regular DNS server code.

caveat: Although I've made changes to the packaging script, I have not
tested them, and I don't intend to, for I don't plan to ever create
another BOSH release, and that breaks my 💔.

bosh-release/packages/sslip.io-dns-server/packaging

@@ -3,6 +3,6 @@ set -ex
 source /var/vcap/packages/golang-1-linux/bosh/compile.env
 
 mkdir src ${BOSH_INSTALL_TARGET}/bin
-mv go.* main.go xip src
-cd src
+mv sslip.io-dns-server/{go.*,main.go,xip} src/
+cd src/
 go build -o ${BOSH_INSTALL_TARGET}/bin/sslip.io-dns-server

ci/pipeline-sslip.io.yml

@@ -25,7 +25,7 @@ jobs:
       inputs:
       - name: sslip.io
       run:
-        dir: sslip.io/src
+        dir: sslip.io/src/sslip.io-dns-server
         path: ginkgo
         args:
         - -r