add a jenkinsfile for updating homebrew openssl on jenkins builders (#3630)

diff --git a/.jenkins/Jenkinsfile-Update-Homebrew-OpenSSL b/.jenkins/Jenkinsfile-Update-Homebrew-OpenSSL
new file mode 100644
index 0000000..33bf751
--- /dev/null
+++ b/.jenkins/Jenkinsfile-Update-Homebrew-OpenSSL
@@ -0,0 +1,35 @@
+def configs = ["sierra", "yosemite"]
+
+def build(label) {
+    node(label) {
+        try {
+            timeout(time: 30, unit: 'MINUTES') {
+                stage("Compile") {
+                    sh """
+                        set -xe
+
+                        /usr/local/bin/brew update
+                        /usr/local/bin/brew reinstall openssl@1.1 --build-bottle
+                    """
+                }
+            }
+        } finally {
+            deleteDir()
+        }
+    }
+}
+
+def builders = [:]
+
+for (_label in configs) {
+    def label = _label
+    builders[label] = {
+        build(label)
+    }
+}
+
+parallel builders
+
+/* We'd like to trigger a downstream job, but bugs. Commented out for now */
+/* Re-enable when the exception from https://ci.cryptography.io/job/cryptography-update-brew-openssl/6/console is fixed */
+/* build job: 'pyca/cryptography/master', wait: false */