Add support for `spk keygen` and `spk getkey` commands
Add support for `spk keygen` and `spk getkey` commands

These are needed for the signing key migration instructions.

ndarilek/vagrant-spk,ndarilek/vagrant-spk,sandstorm-io/vagrant-spk,dwrensha/vagrant-spk,ndarilek/vagrant-spk,sandstorm-io/vagrant-spk,dwrensha/vagrant-spk,dwrensha/vagrant-spk,sandstorm-io/vagrant-spk