Create server failed because of the losing of root_gb in node info

Description
===========
When using latest mogan to create baremetal servers, all failed.

Steps to reproduce
===========
Using openstack baremetalcompute server create mogan --flavor 2a13f1f9-962e-4b73-84f2-6179fe7f56cd --image 5dac1b27-636a-4fb8-978f-c074c76e3743 --nic net-id=630bfdd2-0bfd-40ce-a054-4e0ae9f95b43

Then, you would found the server became error

Mogan commit
commit cb02f1c19ba460d1c5c6b8851a21d9948bad3e0e
Merge: a8050e3 7d67f24
Author: Zuul <email address hidden>
Date: Wed Nov 1 11:11:20 2017 +0000

    Merge "Zuul: add file extension to playbook path"

Logs
==============
     |__Atom 'mogan.engine.flows.create_server.OnFailureRescheduleTask;server:create' {'intention': 'EXECUTE', 'state': 'SUCCESS', 'requires': {'request_spec': {u'availability_zone': None, u'server_properties': {u'flavor_uuid': u'2a13f1f9-962e-4b73-84f2-6179fe7f56cd', u'networks': [{u'net_id': u'630bfdd2-0bfd-40ce-a054-4e0ae9f95b43'}]}, u'num_servers': 1, u'server_ids': ['3bece9a0-4e20-4010-bbc5-7e0f0941db78'], u'flavor': {u'resource_traits': {}, u'uuid': u'2a13f1f9-962e-4b73-84f2-6179fe7f56cd', u'created_at': u'2017-11-02T07:39:04.000000', u'updated_at': None, u'name': u'baremetal_1cpu_1024mbram_10gbdisk', u'disabled': False, u'resources': {u'baremetal': u'1'}, u'is_public': True, u'resource_aggregates': {}, u'projects': [], u'description': u'CPU: 1, RAM: 1024MB, DISK: 10GB'}, u'scheduler_hints': {}}, 'requested_networks': [{u'net_id': u'630bfdd2-0bfd-40ce-a054-4e0ae9f95b43'}], 'context': <oslo_context.context.RequestContext object at 0x7f6276604cd0>, 'filter_properties': {'retry': {u'num_attempts': 3, u'nodes': [u'c002878f-972e-417b-ab89-f5966d981ec6', u'772057e3-17a5-4c58-9891-ab5ce9ca8ce4', u'c002878f-972e-417b-ab89-f5966d981ec6'], u'exc': [u'Traceback (most recent call last):\n', u' File "/usr/local/lib/python2.7/dist-packages/taskflow/engines/action_engine/executor.py", line 53, in _execute_task\n result = task.execute(**arguments)\n', u' File "/opt/stack/mogan/mogan/engine/flows/create_server.py", line 274, in execute\n self.driver.spawn(context, server, configdrive_value, partitions)\n', u' File "/opt/stack/mogan/mogan/baremetal/ironic/driver.py", line 308, in spawn\n \'power\': validate_chk.power})\n', u'ValidationError: Ironic node: 772057e3-17a5-4c58-9891-ab5ce9ca8ce4 failed to validate. (deploy: {u\'reason\': u"Cannot validate driver deploy. Some parameters were missing in node\'s instance_info. Missing are: [\'root_gb\']", u\'result\': False}, power: {u\'result\': True})\n']}}, 'user_data': None, 'server': Server(affinity_zone=None,availability_zone=None,created_at=2017-11-02T09:04:49Z,description=None,fault=<?>,flavor_uuid=2a13f1f9-962e-4b73-84f2-6179fe7f56cd,id=11,image_uuid=5dac1b27-636a-4fb8-978f-c074c76e3743,key_name=None,launched_at=None,locked=False,locked_by=None,metadata={},name='mogan',nics=ServerNics,node='node-1',node_uuid=c002878f-972e-417b-ab89-f5966d981ec6,partitions={},power_state=None,project_id=602626b119ca4268b0227f67b3dde653,status='building',updated_at=None,user_id=b4b3577840134508931567c200c2332d,uuid=3bece9a0-4e20-4010-bbc5-7e0f0941db78), 'key_pair': None, 'injected_files': [], 'partitions': None}, 'provides': None}
        |__Flow 'server_create_manager'^[[00m: ValidationError: Ironic node: c002878f-972e-417b-ab89-f5966d981ec6 failed to validate. (deploy: {u'reason': u"Cannot validate driver deploy. Some parameters were missing in node's instance_info. Missing are: ['root_gb']", u'result': False}, power: {u'result': True})
2017-11-02 17:05:09.316 TRACE mogan.engine.manager ^[[01;35m^[[00mTraceback (most recent call last):
2017-11-02 17:05:09.316 TRACE mogan.engine.manager ^[[01;35m^[[00m File "/usr/local/lib/python2.7/dist-packages/taskflow/engines/action_engine/executor.py", line 53, in _execute_task
2017-11-02 17:05:09.316 TRACE mogan.engine.manager ^[[01;35m^[[00m result = task.execute(**arguments)
2017-11-02 17:05:09.316 TRACE mogan.engine.manager ^[[01;35m^[[00m File "/opt/stack/mogan/mogan/engine/flows/create_server.py", line 274, in execute
2017-11-02 17:05:09.316 TRACE mogan.engine.manager ^[[01;35m^[[00m self.driver.spawn(context, server, configdrive_value, partitions)
2017-11-02 17:05:09.316 TRACE mogan.engine.manager ^[[01;35m^[[00m File "/opt/stack/mogan/mogan/baremetal/ironic/driver.py", line 308, in spawn
2017-11-02 17:05:09.316 TRACE mogan.engine.manager ^[[01;35m^[[00m 'power': validate_chk.power})
2017-11-02 17:05:09.316 TRACE mogan.engine.manager ^[[01;35m^[[00mValidationError: Ironic node: c002878f-972e-417b-ab89-f5966d981ec6 failed to validate. (deploy: {u'reason': u"Cannot validate driver deploy. Some parameters were missing in node's instance_info. Missing are: ['root_gb']", u'result': False}, power: {u'result': True})