Ensure start time is earlier than end time in simple_tenant_usage

Simple check and respond with a http 400 if the start time is later

Fixes LP# 1118910

Change-Id: I95f12abca725f347488e620d8c699f424e53ed23
Speedup the revert_state test

test_revert_state can take over 10 seconds, but more than half of the
time is spent in run_instance() which doesn't change the result.
Remove the call to speed up the tests.

Change-Id: I0557d6822576b99376da8691ee6e76b759d3bc9c
Merge "Speedup the revert_state test"
Merge "Ensure start time is earlier than end time in simple_tenant_usage"