'Parse volume_type\'s extra_specs table for a violin-specific key.
:param volume:  volume object containing volume_type to query
:param spec_key:  the metadata key to search for
:returns: string value associated with spec_key'

def _get_violin_extra_spec(self, volume, spec_key):

    spec_value = None
    ctxt = context.get_admin_context()
    typeid = volume['volume_type_id']
    if typeid:
        volume_type = volume_types.get_volume_type(ctxt, typeid)
        volume_specs = volume_type.get('extra_specs')
        for (key, val) in volume_specs.items():
            if (':' in key):
                scope = key.split(':')
                key = scope[1]
                if ((scope[0] == 'violin') and (key == spec_key)):
                    spec_value = val
                    break
    return spec_value
