Pull keyring storage password from an environment variable.

[krpatter-intc]

I'm trying to use this backend with PIP but the fact that the storage the password is always prompted for, breaks when pip prompts keyring for the actual password.

Is there a way to provide the storage password without user input? The readme shows an environment variable, but I think that's just an example for how a script could use it. Pip is always a process/subprocess so I dont have control of setting it in that manner.