Move to use "get_password" instead of "{user,service,db}_password"

The user_password, service_password and db_password functions are redundant
since they simply call "secret". Creates a get_password function that
will accept a "type" of db, service or user.

All instances of these calls have been changed to call get_password.

Change-Id: I376297b7b8995d5c706e27a4388d2352343861db
Partial-Bug: #1195915