JcloudsLocation: using password for login

- extract credentials from AdminAccess if that was used to set up the
  user.
- don't tell jclouds to lockSsh if using password-based login
  (as that disables password-login!)
- re-enable JcloudsLoginLiveTests
Jclouds computeService cache: only reuse if same provider

- include provider+identity+credential in cache key, so only
  reuses the computeService if it really is for the desired provider!