Remove dependency of test_v1_api on other tests

test_v1_api would fail if run by itself. A config value was
apparently being set by another test so that this test would
pass if run as part of the whole suite but not alone.

Specifically, the missing value was 'backend' in group 'database'.

This patch imports the 'backend' option in base.py which is the
base of test_v1_api.

Change-Id: I37d72398050057def6a378e03c14a9a4eeb55a16
Closes-bug: #1283242
Merge "Remove dependency of test_v1_api on other tests"