orchestration: switch deferred_auth_method to 'password'

Before, 'trusts' was set by default but it requires Keystone API v3.
Since we are still working on Icehouse, let's use 'password' which
supports Keystone API v2.
Merge pull request #720 from enovance/fix-deferred_auth_method

orchestration: switch deferred_auth_method to 'password'