Pass command-line args to server() function

So that the daemon can open the keyring file with --keyring-pin and --entry-pin
options.

Also remove some unused code.
Env vars SERVAL_KEYRING_PATH and SERVAL_KEYRING_READONLY

To support release signing operations without having to copy the release
keyring from its USB stick (into an instance directory), and reducing
the risk of corrupting the release keyring file while using it in-place.
Work around broken Vim syntax highlighting
Improve keyring environment variables

Rename to SERVALD_...

Interpret SERVALD_KEYRING_PATH relative to instance dir unless absolute.

Explicitly unset them in setup_servald() test defs function
Add tests for new keyring environment vars