Fix extension parameters in test_multiple_create

In create() method of server, nova API parses extension parameters
from each extension's server_create() method by the following call:

   self.create_extension_manager.map(self._create_extension_point,
                                     server_dict, create_kwargs)

block_device_mapping value is parsed from 'os-block-device-mapping:
block_device_mapping' in os-block-device-mapping extension, and
min_count value is done from 'os-multiple-create:min_count'.
This patch fixes some wrong extension parameters in unit tests.

os-block-device-mapping extension calls BlockDeviceDict.from_api()
method for getting bdm_type and uuid from "source_type" and "uuid",
but current these parameters also are wrong.
This patch fixes test block_device_mapping values also.

These bugs were found through jsonschema validation framework
development, because the framework doesn't allow undefined
parameters based on each schema.

Change-Id: I0d5899c84c7a7f2938a553d7ce845f855f1dfd7a
Merge "Fix extension parameters in test_multiple_create"