Share CreateBackup unit test between V2 & V2.1

This patch moves CreateBackup unit test from v3 directory to contrib
and makes it shared by V2 and V21.

PS. create_backup unit test cases was removed from admin actions unit
test case.

Partially implements blueprint v2-on-v3-api
Change-Id: I607acc7406f8538a644749f9fb218d160e3e306d
Merge "Share CreateBackup unit test between V2 & V2.1"