execution-update command doesn't work

[Anastasia Kuznetsova]

Steps to reproduce:
1. Create following workflow:
---
version: "2.0"
wf_main:
  tasks:
    invoke_wf:
      with-items:
       - i in [1,2,3,4,5,6,7,8,9]
      workflow: wf_work var="<% $.i %>"
      publish:
        res: <% $.invoke_wf %>

wf_work:
  input:
    - var
  output:
    var: <% $.echo %>
  tasks:
    echo:
      action: std.echo output=<% $.var %>

2. Execute "mistral execution-create wf_main"
3. Execute "mistral execution-update <exec_id> ERROR"

Observed result:
'module' object has no attribute 'DBError'
2015-04-28 13:09:03.939 2138 ERROR oslo_messaging._drivers.common [-] Returning exception (ProgrammingError) (1064, "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '} WHERE executions_v2.id = 'e48920ea-871e-4892-836c-ce9fa6c36c64'' at line 1") 'UPDATE executions_v2 SET updated_at=%s, state_info=%s WHERE executions_v2.id = %s' (datetime.datetime(2015, 4, 28, 13, 9, 3, 930547), {}, 'e48920ea-871e-4892-836c-ce9fa6c36c64')

NOTE:
Another scenario:
SUCCESS - > RUNNING
'NoneType' object has no attribute 'to_dict'
Traceback (most recent call last):

  File "/usr/local/lib/python2.7/dist-packages/wsmeext/pecan.py", line 82, in callfunction
    result = f(self, *args, **kwargs)

  File "/home/ubuntu/mistral/mistral/api/controllers/v2/execution.py", line 162, in put
    wf_ex if isinstance(wf_ex, dict) else wf_ex.to_dict()

AttributeError: 'NoneType' object has no attribute 'to_dict'

[Nikolay Makhotkin (nmakhotkin)]

However, resume command works fine:

  mistral execution-update <id> RUNNING

it successfully resumes workflow execution.

[Nikolay Makhotkin (nmakhotkin)]

Pasue cmd also works as designed.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/185013

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/185013
Committed: https://git.openstack.org/cgit/stackforge/mistral/commit/?id=3b16cd8dd2f4a995deac07031645885a12465fb6
Submitter: Jenkins
Branch: master

commit 3b16cd8dd2f4a995deac07031645885a12465fb6
Author: Nikolay Mahotkin <email address hidden>
Date: Fri May 22 16:03:42 2015 +0300

    Fixing execution-update API

     * Fixed handling wrong using execution-update
     * Fixed session hanging in case incorrect using execution update API:
         in case of exception neither commit_tx nor rollback_tx has not
         been invoked -> session acquired semaphore but didn't release it.
       Note: it is related only to sqlite (used in unit tests).

    Closes-Bug: #1449557

    Change-Id: Ic8874b2d498167cac1a88f6d138e8ac0e1d9a67f