Get workbook definition if workbook doesn't exist returns 500 code

[Nikolay Makhotkin]

Steps to reproduce:

1. Run client
2. type "workbook-get-definition some-workbook-name"
3. See Server Error, while 404 expected

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/93886

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/95626
Committed: https://git.openstack.org/cgit/stackforge/mistral/commit/?id=5e9ffd5c479260367b4be5d9d26f147a85c010a8
Submitter: Jenkins
Branch: master

commit 5e9ffd5c479260367b4be5d9d26f147a85c010a8
Author: Angus Salkeld <email address hidden>
Date: Tue May 27 16:23:00 2014 +1000

    Cleanup exceptions and add http code

    - Remove redundant constructors
    - always use "code" as an http_status
    - fix the default message strings so you can pass nothing into the
      exception constructor and it will work.
    - add some basic tests

    Partial-bug: #1320136
    Co-Authored-By: Nikolay Mahotkin <email address hidden>

    Change-Id: I9e21c6d5d39f1203324a37a39e5fd6069062b733

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/93886
Committed: https://git.openstack.org/cgit/stackforge/mistral/commit/?id=1ceb4b1e8ac2c49f1f458c804f5c1f8269b829a7
Submitter: Jenkins
Branch: master

commit 1ceb4b1e8ac2c49f1f458c804f5c1f8269b829a7
Author: Angus Salkeld <email address hidden>
Date: Wed May 28 12:38:40 2014 +1000

    Add/Fix all error handling mechanism on REST API

     * Refactor error handling
     * add tests for correct error codes

    Closes bug: #1320136
    Co-Authored-By: Angus Salkeld <email address hidden>
    Change-Id: Ia33e19cab4879164acb7c8268c9c657f4196df45