make admin access work with one username/password

[glenfarclas17]

Currently to use d3admin, the user must provide two usernames and three passwords, which are stored in the keychain.

API => user/passwd SQL => user/passwd MasterDistPoint => passwd

Devise a method for securely storing enough data in the JSS, accessible via the API, limited to the d3admin, to get the other passwords as needed.

Then store only the API username/passwd in the local keychain, possibly with one other key, for decryption.

Possible with ideas based on: https://github.com/jamfit/Encrypted-Script-Parameters