Jenkinsfile: force validate steps on master and backports

On master ("non-pull-request"), force running some validation checks
(such as vendor, swagger), even if no files were changed. This allows
catching problems caused by pull-requests that were merged out-of-sequence.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Jenkinsfile

@@ -9,6 +9,7 @@ pipeline {
     }
     parameters {
         booleanParam(name: 'unit_validate', defaultValue: true, description: 'amd64 (x86_64) unit tests and vendor check')
+        booleanParam(name: 'validate_force', defaultValue: false, description: 'force validation steps to be run, even if no changes were detected')
         booleanParam(name: 'amd64', defaultValue: true, description: 'amd64 (x86_64) Build/Test')
         booleanParam(name: 'arm64', defaultValue: true, description: 'ARM (arm64) Build/Test')
         booleanParam(name: 's390x', defaultValue: true, description: 'IBM Z (s390x) Build/Test')
@@ -62,6 +63,12 @@ pipeline {
                         expression { params.unit_validate }
                     }
                     agent { label 'amd64 && ubuntu-1804 && overlay2' }
+                    environment {
+                        // On master ("non-pull-request"), force running some validation checks (vendor, swagger),
+                        // even if no files were changed. This allows catching problems caused by pull-requests
+                        // that were merged out-of-sequence.
+                        TEST_FORCE_VALIDATE = sh returnStdout: true, script: 'if [ "${BRANCH_NAME%%-*}" != "PR" ] || [ "${CHANGE_TARGET:-master}" != "master" ] || [ "${validate_force}" = "true" ]; then echo "1"; fi'
+                    }
 
                     stages {
                         stage("Print info") {
@@ -90,6 +97,7 @@ pipeline {
                                   -e DOCKER_EXPERIMENTAL \
                                   -e DOCKER_GITCOMMIT=${GIT_COMMIT} \
                                   -e DOCKER_GRAPHDRIVER \
+                                  -e TEST_FORCE_VALIDATE \
                                   -e VALIDATE_REPO=${GIT_URL} \
                                   -e VALIDATE_BRANCH=${CHANGE_TARGET} \
                                   docker:${GIT_COMMIT} \
@@ -197,6 +205,7 @@ pipeline {
                                   -e DOCKER_EXPERIMENTAL \
                                   -e DOCKER_GITCOMMIT=${GIT_COMMIT} \
                                   -e DOCKER_GRAPHDRIVER \
+                                  -e TEST_FORCE_VALIDATE \
                                   -e VALIDATE_REPO=${GIT_URL} \
                                   -e VALIDATE_BRANCH=${CHANGE_TARGET} \
                                   docker:${GIT_COMMIT} \