Set TEST_MODE true for dev envs

[paulbynd]

Per @rtshadow's comment on #72, enable TEST_MODE when in dev_appserver to avoid an otherwise confusing and fatal error later.

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[paulbynd]

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[blech]

I'll admit that this is a hack rather than a well tested solution, and I suspect @cjfuller's fix, or instead a better resolution of the underlying #71 issue, would be better. Thanks for commenting, and perhaps I'll try running with an explicit app and version name and see if that avoids the issue.