* add dev flag to override pgp key for plugin signature verification
-dev-plugin-pgp-key is the path to a PGP public key file to use for
plugin signature verification in dev mode. This prevents developers from
having to manually hard code their own pgp key into vault source code
and rebuild vault to develop and test enterprise plugins.
* fix sync once error handling
* add tests
* remove test
* tests: set random listener addr
* improve error message
* dedupe getVerifyFunc annd verifyPGPSignatureDetached
* accept raw key as well as path
* keep hc key and add custom key to keyring
Co-authored-by: John-Michael Faircloth <fairclothjm@users.noreply.github.com>
