Improve account testing in handler_tests.py
Improve account testing in handler_tests.py

Use functions with clear names to switch the authentication mode in the test
case. It makes the tests much more obvious in their behavior.

This helps catch the subtlety in the different access control levels.

R=csharp@chromium.org
BUG=

Review URL: https://codereview.appspot.com/133870045

madecoste/swarming,luci/luci-py,luci/luci-py,luci/luci-py,luci/luci-py,madecoste/swarming,pombreda/swarming,pombreda/swarming,madecoste/swarming,pombreda/swarming,madecoste/swarming,pombreda/swarming