Do not obscure Unauthorized error messages

All Unauthorized exceptions are currently trapped and
the following message is printed:
    Invalid OpenStack Identity credentials.

This is unhelpful now that heat-api is providing structured
errors with (sometimes) helpful context for authorization failures.

This change removes this error trapping and prints the intended
error message.

Change-Id: Ibd943deb1f365e5f212225be1e675beb14accf97
Merge "Do not obscure Unauthorized error messages"