Fix PatchStacktraceTest for pypy
Fix PatchStacktraceTest for pypy

test_trace test cannot pass with mocked do_execute on pypy
environment. Allow test to call do_execute with correct sql
query.

Change-Id: I165fc4de9f4a7f10cb45e92301652224e63f113b

magic0704/oslo.db,openstack/oslo.db,openstack/oslo.db