Passphrase attempt and errorring logic for keys could be improved

[riyazdf]

I was doing some local testing when I realized that it's possible to fail > attempts times on passphrases that are too short, but then notary will fail with ErrAttemptsExceeded after inputting a valid passphrase. While most users may not run into this exact failure case, I think we could revisit and improve the passphrase attempt logic UX at the KeyStore level in general

🐳 $ bin/notary init repo
Root key found, using: 4327a8deba2cae19a4b393d2c6cf3a2f349652c84bc41bc1e09ade182d86b19a
Enter passphrase for root key with ID 4327a8d:
Enter passphrase for new targets key with ID f511f86 (repo):
Passphrase is too short. Please use a password manager to generate and store a good random passphrase.
Enter passphrase for new targets key with ID f511f86 (repo):
Passphrase is too short. Please use a password manager to generate and store a good random 
...
[truncated]
...
Enter passphrase for new targets key with ID f511f86 (repo):
Passphrase is too short. Please use a password manager to generate and store a good random passphrase.
Enter passphrase for new targets key with ID f511f86 (repo):
Repeat passphrase for new targets key with ID f511f86 (repo):

* fatal: failed to add key to filestore: maximum number of passphrase attempts exceeded