Should raise error if hooks is invalid

[huangtianhua]

Test the blueprint: https://blueprints.launchpad.net/heat/+spec/stack-breakpoint
1. set hooks for resource breakpoint in environment file:
   resource_registry:
      resources:
         my_server:
             hooks: pre-cre
2. expected to pause on server creation, but nothing happen and no pause, and user may don't know why

3. I think if hooks are invalid, we should raise error message to user, such as 'Invalid hook type "pre-cre" for resource breakpoint, acceptable hooks: "pre-create", "pre-update"', then user will know what happen.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/183409

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/183409
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=bffee054a1e9d2c3eb100bac319000013223d101
Submitter: Jenkins
Branch: master

commit bffee054a1e9d2c3eb100bac319000013223d101
Author: huangtianhua <email address hidden>
Date: Fri May 15 14:58:03 2015 +0800

    Should raise error if hook is invalid

    If hooks of resource breakpoint are invalid, should
    raise error message to user, and then user will know
    what happen and why no pause on updation/creation.

    Change-Id: I53822ed96fafdd373d20c45cacb5e33ba0306292
    Closes-Bug: #1452636