is_public should be checked when creating volume type

[Liyingjun]

DBError will be raised if we specify a non boolean value for is_public when creating volume type.

$ curl -g -i -X POST http://192.168.70.11:8776/v2/a0a74317a58b479290492ebc96b5019d/types -H "User-Agent: python-cinderclient" -H "Content-Type: application/json" -H "Accept: application/json" -H "X-Auth-Token: d8fe2654b94f459282ad02c5671b8826" -d '{"volume_type": {"os-volume-type-access:is_public": "xxx", "name": "test6", "description": "test6"}}'

Part of log from cinder-api.log
DB exception wrapped.
2015-07-29 09:09:08.752 TRACE oslo_db.sqlalchemy.exc_filters Traceback (most recent call last):
2015-07-29 09:09:08.752 TRACE oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 889, in _execute_context
2015-07-29 09:09:08.752 TRACE oslo_db.sqlalchemy.exc_filters context = constructor(dialect, self, conn, *args)
2015-07-29 09:09:08.752 TRACE oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 573, in _init_compiled
2015-07-29 09:09:08.752 TRACE oslo_db.sqlalchemy.exc_filters param.append(processors[key](compiled_params[key]))
2015-07-29 09:09:08.752 TRACE oslo_db.sqlalchemy.exc_filters File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/processors.py", line 56, in boolean_to_int
2015-07-29 09:09:08.752 TRACE oslo_db.sqlalchemy.exc_filters return int(value)
2015-07-29 09:09:08.752 TRACE oslo_db.sqlalchemy.exc_filters ValueError: invalid literal for int() with base 10: 'xxx'

Full log: http://paste.openstack.org/show/406153/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/206784