ci: adapt to new buildroot image

We're moving away from a buildroot image based on cosa, so we need to do
our build in a separate pod. This is more complex, but the upside is
that it guarantees that we're always building in the same buildroot that
was used to build all of FCOS' components.

.cci.jenkinsfile

@@ -1,17 +1,37 @@
 // Documentation: https://github.com/coreos/coreos-ci/blob/master/README-upstream-ci.md
 
-cosaPod(buildroot: true) {
+buildPod {
     checkout scm
 
     // hack to satisfy golang compiler wanting to cache things
     shwrap("mkdir cache")
     withEnv(["XDG_CACHE_HOME=${env.WORKSPACE}/cache"]) {
+        // XXX: convert all this to coreos-ci-lib sugar
+        stage("Build") {
+            shwrap("make")
+            shwrap("make install DESTDIR=install")
+            stash name: 'build', includes: 'install/**'
+        }
         // first, run gofmt/govet/unit tests
         stage("Unit Tests") {
             shwrap("./test")
         }
-        fcosBuild(make: true, skipKola: true)
+        stage("Build Blackbox Tests") {
+            shwrap("""
+                ./build_blackbox_tests
+                mkdir -p tests/kola/blackbox/data/bin
+                mv tests.test bin/amd64/*-stub tests/kola/blackbox/data/bin
+            """)
+            stash name: 'blackbox', includes: 'tests/kola/blackbox/data/bin/**'
+        }
     }
+}
+
+cosaPod {
+    checkout scm
+
+    unstash name: 'build'
+    fcosBuild(skipKola: true, overlays: ["install"])
 
     // we run the blackbox tests separately instead of as part of the main kola
     // run since it's a distinct kind of test and we want to draw more
@@ -21,11 +41,7 @@ cosaPod(buildroot: true) {
     fcosKola(extraArgs: "--denylist-test ext.*")
 
     parallel blackbox: {
-        shwrap("""
-            ./build_blackbox_tests
-            mkdir -p tests/kola/blackbox/data
-            mv tests.test bin tests/kola/blackbox/data
-        """)
+        unstash name: 'blackbox'
         fcosKola(extraArgs: "--tag external", skipUpgrade: true)
     }, testiso: {
         try {

tests/kola/blackbox/run.sh

@@ -1,5 +1,5 @@
 #!/bin/bash
 set -euo pipefail
 
-export PATH=${KOLA_EXT_DATA}/bin/amd64:$PATH
-exec ${KOLA_EXT_DATA}/tests.test
+export PATH=${KOLA_EXT_DATA}/bin:$PATH
+exec ${KOLA_EXT_DATA}/bin/tests.test