Cirrus: Skip rebuilding images unless instructed

Given frequent merges, it doesn't make sense to rebuild the VM testing
images every time.  Instead, monitor the PR title and description for
a magic string, only triggering builds on a match:

***CIRRUS: REBUILD IMAGES***

Signed-off-by: Chris Evich <cevich@redhat.com>

2 files changed, 26 insertions, 12 deletions

diff --git a/contrib/cirrus/build_vm_images.sh b/contrib/cirrus/build_vm_images.sh
index 80c689a6c..ffbb2d5d5 100755
--- a/contrib/cirrus/build_vm_images.sh
+++ b/contrib/cirrus/build_vm_images.sh
@@ -22,9 +22,7 @@ SCRIPT_BASE $SCRIPT_BASE
 PACKER_BASE $PACKER_BASE
 "
 
-# TODO: Skip building images if $CIRRUS_BRANCH =~ "master" and
-# commit message of $CIRRUS_CHANGE_IN_REPO contains a magic word
-# produced by 'commit_and_create_upstream_pr.sh' script (see .cirrus.yml)
+require_regex '\*\*\*\s*CIRRUS:\s*REBUILD\s*IMAGES\s*\*\*\*' 'Not re-building VM images'
 
 show_env_vars
 
diff --git a/contrib/cirrus/lib.sh b/contrib/cirrus/lib.sh
index 1e0052a65..12d24042f 100644
--- a/contrib/cirrus/lib.sh
+++ b/contrib/cirrus/lib.sh
@@ -117,6 +117,22 @@ cdsudo() {
     sudo --preserve-env=GOPATH --non-interactive bash -c "$CMD"
 }
 
+# Skip a build if $1 does not match in the PR Title/Description with message $2
+require_regex() {
+    req_env_var "
+        CIRRUS_CHANGE_MESSAGE $CIRRUS_CHANGE_MESSAGE
+        1 $1
+        2 $2
+    "
+    regex="$1"
+    msg="$2"
+    if ! echo "$CIRRUS_CHANGE_MESSAGE" | egrep -q "$regex"
+    then
+        echo "***** The PR Title/Description did not match the regular expression: $MAGIC_RE"
+        echo "***** $msg"
+        exit 0
+    fi
+}
 
 # Helper/wrapper script to only show stderr/stdout on non-zero exit
 install_ooe() {
@@ -142,8 +158,8 @@ EOF
 install_cni_plugins() {
     echo "Installing CNI Plugins from commit $CNI_COMMIT"
     req_env_var "
-    GOPATH $GOPATH
-    CNI_COMMIT $CNI_COMMIT
+        GOPATH $GOPATH
+        CNI_COMMIT $CNI_COMMIT
     "
     DEST="$GOPATH/src/github.com/containernetworking/plugins"
     rm -rf "$DEST"
@@ -160,9 +176,9 @@ install_runc(){
     echo "Installing RunC from commit $RUNC_COMMIT"
     echo "Platform is $OS_RELEASE_ID"
     req_env_var "
-    GOPATH $GOPATH
-    RUNC_COMMIT $RUNC_COMMIT
-    OS_RELEASE_ID $OS_RELEASE_ID
+        GOPATH $GOPATH
+        RUNC_COMMIT $RUNC_COMMIT
+        OS_RELEASE_ID $OS_RELEASE_ID
     "
     if [[ "$OS_RELEASE_ID" =~ "ubuntu" ]]; then
         echo "Running make install.libseccomp.sudo for ubuntu"
@@ -202,8 +218,8 @@ install_buildah() {
 install_conmon(){
     echo "Installing conmon from commit $CRIO_COMMIT"
     req_env_var "
-    GOPATH $GOPATH
-    CRIO_COMMIT $CRIO_COMMIT
+        GOPATH $GOPATH
+        CRIO_COMMIT $CRIO_COMMIT
     "
     DEST="$GOPATH/src/github.com/kubernetes-sigs/cri-o.git"
     rm -rf "$DEST"
@@ -234,8 +250,8 @@ install_criu(){
 install_testing_dependencies() {
     echo "Installing ginkgo, gomega, and easyjson into \$GOPATH=$GOPATH"
     req_env_var "
-    GOPATH $GOPATH
-    GOSRC $GOSRC
+        GOPATH $GOPATH
+        GOSRC $GOSRC
     "
     cd "$GOSRC"
     ooe.sh go get -u github.com/onsi/ginkgo/ginkgo