Description of problem:
-----------------------
Attempt to 'cancel' overcloud update reports error when operator requests to cancel update:

openstack overcloud update stack -i overcloud
Started Mistral Workflow tripleo.package_update.v1.package_update_plan. Execution ID: 433009fe-2c10-4241-8f48-a9c6c46a9f38
Waiting for messages on queue 'dd8e32d7-0216-465c-9210-86cbca6c8513' with no timeout.
WAITING
not_started: [u'ceph-2']
on_breakpoint: [u'compute-0', u'controller-2', u'ceph-0', u'controller-0', u'ceph-1', u'controller-1']
Breakpoint reached, continue? Regexp or Enter=proceed (will clear 60595c23-63e8-47d3-91d7-6e2b40f8f322), no=cancel update, C-c=quit interactive mode: 
IN_PROGRESS
WAITING
completed: [u'controller-1']
on_breakpoint: [u'ceph-2', u'compute-0', u'ceph-0', u'controller-0', u'ceph-1', u'controller-2']
Breakpoint reached, continue? Regexp or Enter=proceed (will clear 3211202f-0582-40e4-a242-3ded79ba2be6), no=cancel update, C-c=quit interactive mode: 
IN_PROGRESS
WAITING
completed: [u'controller-2', u'controller-1']
on_breakpoint: [u'compute-0', u'ceph-1', u'controller-0', u'ceph-2', u'ceph-0']
Breakpoint reached, continue? Regexp or Enter=proceed (will clear 9cc1f1f1-74a6-48dd-bc9f-4717e0287219), no=cancel update, C-c=quit interactive mode: 
IN_PROGRESS
WAITING
completed: [u'controller-2', u'controller-1', u'ceph-0']
on_breakpoint: [u'ceph-1', u'controller-0', u'ceph-2', u'compute-0']
Breakpoint reached, continue? Regexp or Enter=proceed (will clear e2176598-d109-4e5a-aea3-afa7c8ef3e5a), no=cancel update, C-c=quit interactive mode: 
WAITING
completed: [u'controller-2', u'compute-0', u'controller-1', u'ceph-0']
on_breakpoint: [u'ceph-1', u'controller-0', u'ceph-2']
Breakpoint reached, continue? Regexp or Enter=proceed (will clear 21a484f6-f906-4876-b946-1010ead62325), no=cancel update, C-c=quit interactive mode: cancel
WAITING
completed: [u'controller-2', u'compute-0', u'controller-1', u'ceph-0']
on_breakpoint: [u'ceph-1', u'controller-0', u'ceph-2']
Breakpoint reached, continue? Regexp or Enter=proceed (will clear 21a484f6-f906-4876-b946-1010ead62325), no=cancel update, C-c=quit interactive mode: no
canceling update, doing rollback
WAITING
on_breakpoint: [u'ceph-2', u'compute-0', u'controller-2', u'ceph-0', u'controller-0', u'ceph-1', u'controller-1']
Breakpoint reached, continue? Regexp or Enter=proceed (will clear 60595c23-63e8-47d3-91d7-6e2b40f8f322), no=cancel update, C-c=quit interactive mode: no
canceling update, doing rollback
ERROR: Cancelling update when stack is ROLLBACK_IN_PROGRESS is not supported.

openstack stack list
+--------------------------------------+------------+----------------------+----------------------+----------------------+
| ID                                   | Stack Name | Stack Status         | Creation Time        | Updated Time         |
+--------------------------------------+------------+----------------------+----------------------+----------------------+
| 1ca3a4ca-ff75-497c-8fea-2caa097969a6 | overcloud  | ROLLBACK_IN_PROGRESS | 2017-03-01T11:54:17Z | 2017-03-06T06:45:02Z |
+--------------------------------------+------------+----------------------+----------------------+----------------------+

Version-Release number of selected component (if applicable):
-------------------------------------------------------------
openstack-tripleo-heat-templates-6.0.0-0.20170222195630.46117f4.el7ost.noarch
openstack-tripleo-validations-5.4.0-0.20170217125407.6b928f1.el7ost.noarch
openstack-tripleo-puppet-elements-6.0.0-0.20170217130711.3e6bc8c.el7ost.noarch
puppet-tripleo-6.2.0-0.20170222195517.7f91deb.el7ost.noarch
openstack-tripleo-image-elements-6.0.0-0.20170217063119.ad33b59.el7ost.noarch
python-tripleoclient-6.0.1-0.20170220144855.b3c0e3e.el7ost.noarch
openstack-tripleo-ui-3.0.1-0.20170224170804.8f3b43e.el7ost.noarch
openstack-tripleo-common-5.8.1-0.20170220145134.8ff75ce.el7ost.noarch

openstack-mistral-common-4.0.1-0.20170222161147.060a153.el7ost.noarch
python-openstack-mistral-4.0.1-0.20170222161147.060a153.el7ost.noarch
openstack-mistral-engine-4.0.1-0.20170222161147.060a153.el7ost.noarch
puppet-mistral-10.3.0-0.20170213130808.a6e8ebc.el7ost.noarch
openstack-mistral-executor-4.0.1-0.20170222161147.060a153.el7ost.noarch
python-mistralclient-3.0.0-0.20170208192040.a7bf138.el7ost.noarch
openstack-mistral-api-4.0.1-0.20170222161147.060a153.el7ost.noarch

python-heatclient-1.8.0-0.20170208192329.17dd306.el7ost.noarch
openstack-heat-api-8.0.0-0.20170222153633.2dd8335.el7ost.noarch
openstack-heat-api-cfn-8.0.0-0.20170222153633.2dd8335.el7ost.noarch
puppet-heat-10.3.0-0.20170210225040.920f4f9.el7ost.noarch
heat-cfntools-1.3.0-2.el7ost.noarch
python-heat-agent-1.0.0-1.el7ost.noarch
openstack-heat-engine-8.0.0-0.20170222153633.2dd8335.el7ost.noarch
openstack-heat-common-8.0.0-0.20170222153633.2dd8335.el7ost.noarch


Steps to Reproduce:
-------------------
1. Deploy RHOS-11
2. Setup latest repos on undercloud and overcloud
3. Update undercloud
4. Start overcloud update
5. After few nodes are updated request update to cancel

Expected results:
-----------------
Operator is not allowed/asked to cancel update after 'cancel' operation being already requested.

Additional info:
----------------
Virtual setup. Re-run of update operation after failed attemp.