Clean out dead docker containers and docker images every Jenkins build

This will increase build times on Jenkins, but should make the build
times consistent and make them pull from sources every time versus
leftover artifacts. Also upping timeout. (Try to address recent
some aborted builds.)

hack/jenkins/build.sh

@@ -34,16 +34,15 @@ export PATH=$PATH:/usr/local/go/bin
 export KUBE_RELEASE_RUN_TESTS=n
 export KUBE_SKIP_CONFIRMATIONS=y
 
-# Clean stuff out.
-#
-# TODO: Look at git clean plugin again for hermeticism, but may not
-# play nicely with dockerized stuff and permissions. (We may just need
-# to force the build/make-clean.sh at the end of the build regardless
-# of status and be delicate with the exit status.) (Low priority
-# unless there's a hermetic issue.)
+# Clean stuff out. Assume the worst - the last build may have left the
+# tree in an odd state. There's a Jenkins git clean plugin, but we
+# have the docker images to worry about as well, so be really pedantic
+# about cleaning.
 rm -rf ~/.kube*
-./build/make-clean.sh
+make clean
 git clean -fdx
+docker ps -aq | xargs -r docker rm
+docker images -q | xargs -r docker rmi
 
 # Build
 go run ./hack/e2e.go -v --build