VIM should accept valid boolean values for is_default

https://review.openstack.org/570337
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commit b2ac5b6702220f46fd92a51e1c8031bde577e11f
Author: nitesh vanarase <email address hidden>
Date: Tue Jan 23 17:32:26 2018 +0530

    VIM should accept valid boolean values for is_default

    In case of create VIM API, is_default_parameter accepts any string
    values like "abc" or "1234" and set the value as True. It should
    strictly check for valid boolean values.

    Fixed this issue by using convert_to_boolean validator. so now, if
    you pass any non-boolean value, it will return 400 error to the user.

    NOTE:
    The below test case fails if we inherit the test class
    '..tests.unit.base.TestCase' from '..tests.base.BaseTestCase' with
    KeyError:

    tacker.tests.unit.nfvo.test_nfvo_plugin.TestNfvoPlugin.
    test_create_ns_workflow_no_task_exception

    The reason behind the failure is, the raised exception
    '..extensions.nfvo.NoTasksException' expects that the 'action' and
    'resource' should be passed as arguments to the exception while raising
    it to form the exception message. If you don't pass these two arguments
    then it fails to form the exception message and raises KeyError.
    This happens because the '..tests.base.BaseTestCase' test class uses
    exception fixture and sets 'use_fatal_exceptions' to True always which
    results into not raising the raised exception again and it tries to
    form the exception message and pass it to the base class __init__ for
    further processing. It fails and raises KeyError while forming that
    exception message because in 'test_create_ns_workflow_no_task_exception'
    test case these arguments are not passed to the exception while
    raising.

    To fix this test case, passed the required 'action' and 'resource'
    arguments to the exception while raising it.

    DocImpact
    Closes-Bug: #1746538
    Change-Id: Ib533b38a48d31cb26eecdc546b20b0f99beeaa34