syadav2015

I tried to increase the coverage offered by the tests in 3c495f2 and the `go cover tool` reports 84.2% coverage (up from 81.2% in the original commit). After looking at...

@erahn @LeSuisse I've created [a pull request](https://github.com/LeSuisse/vault-gpg-plugin/pull/18) with changes supporting subkeys with the plugin, plus support for revoking keys and subkeys as well as signing identities of keys. It would...