R1:eb397a48b48e

Detect and prompt for passwords on SSH private keys, then strip them

Summary:
Fixes T4356. Currently, if users add a passworded private key to the Passphrase application, we never ask for the password and can not use it later. This makes several changes:

- Prompt for the password.
- Detect passworded private keys, and don't accept them until we can decrypt them.
- Try to decrypt passworded private keys, and tell the user if the password is missing or incorrect.
- Stop further creation of path…