[autotest] fix unittest with mocking devserver.url call

BUG=chromium:251879
TEST=run python site_rpc_interface_unittest.py
DEPLOY=none

Change-Id: I97e51b466efd90b49b3f968841385c97edbdf838
Reviewed-on: https://gerrit.chromium.org/gerrit/59577
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
1 file changed