Do not ask for "Local NervesHub user password" for every command

[ftes]

Problem

For every mix nerves_hub.* command, I have to enter my Local NervesHub user password.

I gather this is the passphrase for my local user certificate.

Can I avoid this?

Ideas

1. Add passphrase to macos keychain (how?)
2. Generate user certificate without a passphrase (how?)

Workaround

mix nerves_hub.user cert export
cd ~/nerves-hub/
tar -xvzf ./nerves_hub-certs.tar.gz
export NERVES_HUB_CERT=`cat ./cert.pem`
export NERVES_HUB_KEY=`cat ./key.pem`