--os-token is unweildy for use with PKI tokens

Commonly used UUID tokens are of a reasonably length to be specified as CLI arguments. However, given the potential length of base64-encoded PKI tokens, this approach becomes unwieldy.

This blueprint would introduce two new options complement the existing OS_TOKEN environment variable and --os-token CLI argument:

    OS_TOKEN_FILE=/abs/path/to/token

    --os-token-file=/abs/path/to/token

If --os-token-file is provided along with OS_TOKEN_FILE, --os-token-file should take precedence.
If either --os-token or OS_TOKEN is provided along with either OS_TOKEN_FILE or --os-token-file, an error should be raised.