Make multiple_create unit tests share between v2 and v2.1

Now there is a lot of duplicated test code between v2 and v2.1 API
tests and it is better to share them for the code cleanup.
This pach makes multiple_create unit tests share.

Partially implements blueprint v2-on-v3-api

Change-Id: Icf646efeaa8e13c6a3ec48e16523122b5af1658d
Merge "Make multiple_create unit tests share between v2 and v2.1"