Hi,
this is how i install gcloud on mac stacks:
export CLOUDSDK_CONFIG=/Users/vagrant/git/.config/
curl -sSL https://sdk.cloud.google.com > /tmp/gcl && sudo bash /tmp/gcl --install-dir=/Users/vagrant/git/gcloud --disable-prompts
then you can use gcloud like this
/Users/vagrant/git/gcloud/google-cloud-sdk/bin/gcloud auth activate-service-account -q --key-file /tmp/key.json