Exit gce kube-up.sh early if openssl is LibreSSL

macOS has an openssl binary, but it's actually LibreSSL, which
doesn't play well with the easyrsa script that cluster/gce/util.sh
uses to generate certs

Instead of waiting until we generate certs to discover easyrsa doesn't
work, consider openssl a prereq for gce, and include a check for the
version string starting with OpenSSL

Also, mirror kube-up.sh's "... calling" output in kube-down.sh

hack/lib/util.sh

@@ -539,7 +539,14 @@ function kube::util::test_openssl_installed {
     if [ "$?" != "0" ]; then
       echo "Failed to run openssl. Please ensure openssl is installed"
       exit 1
+    elif [ "$(openssl version | cut -d\  -f1)" == "LibreSSL" ]; then
+      echo "LibreSSL is not supported. Please ensure openssl points to an OpenSSL binary"
+      if [ "$(uname -s)" == "Darwin" ]; then
+        echo 'On macOS we recommend using homebrew and adding "$(brew --prefix openssl)/bin" to your PATH'
+      fi
+      exit 1
     fi
+
     OPENSSL_BIN=$(command -v openssl)
 }