Duplicate baker pkh in signatory list

[michaelkernaghan]

I imported my baker key tz1TfGsL6o754mfxcntSzDDTh9RrjZVNocjP into Signatory twice.
using:

./signatory-cli import --config ./signatory.yaml --vault yubi

to see the list

./signatory-cli list

Public Key Hash:    tz1gmj9EBXqQqQBmEVaCHBfunPJ67N82YJcz
Vault:              YubiHSM
ID:                 5cfd
Status:             FOUND_NOT_CONFIGURED
*DISABLED*

Public Key Hash:    tz1TfGsL6o754mfxcntSzDDTh9RrjZVNocjP
Vault:              YubiHSM
ID:                 bce7
Status:             ACTIVE
Allowed Operations: [block endorsement generic]
Allowed Kinds:      [delegation endorsement reveal transaction]

Public Key Hash:    tz1TfGsL6o754mfxcntSzDDTh9RrjZVNocjP
Vault:              YubiHSM
ID:                 caa0
Status:             ACTIVE
Allowed Operations: [block endorsement generic]
Allowed Kinds:      [delegation endorsement reveal transaction]

[jevonearth]

Marginally related to #106

The ID: property here represents the identity of a key on yubihsm. I think that yubihsm can import the same secret many times, and it will give a different ID to each (identical) secret. We could have signatory-cli enforce/prevent import of duplicate secrets, but that won't eliminate the possibility of having dupe keys. We should handle this some other way in signatory.

This issue also highlights an inconsistency in the Vault/Key abstraction around ID:. In yubi, ID is the identity of a specific key on the yubiHSM, but on ledger the ID is derived from the root key that is provisioned on the ledger.