Add TestApp::init() for tests that don't need HTTP recording

[jtgeibel]

The unused Uploader::NoOp option is now Uploader::Panic which
panics on any usage. The panic message directs users to initialize the
app with TestApp::with_proxy().

While this adds more panics to the main lib, the application
configuration isn't dynamic and it should be obvious that
Uploader::Panic is not to be used to configure a production
application.

[jtgeibel]

The test suite currently has 33 (of 166 total) tests that need a thread running an HTTP recording proxy. This PR avoids that overhead for 30 of the unnecessary cases. On my machine (with an average of 3 runs each), this reduces my user time from 26.60 to 26.11 seconds. An additional second or two can probably be saved once all test are converted.

[carols10cents]

Nice! I'm into it! The only slight reservation I have is about the names. I'm trying to think of this from the point of view of a new contributor writing some new tests. They have the empty/with_user/with_token axis to choose from, which is mostly pretty clear I think, and this adds the simple/full axis that I'm not sure is as clear.

The proxy change also affects tests that talk to github as well as those that talk to S3, right? The current doc comments on simple only talks about uploading; full talks about generic outgoing HTTP requests though, so that's good.

Some ideas for names, none of which I really like yet but maybe it'll help us get to something good:

• proxy/no_proxy
• record_http/no_record_http
• makes_external_http_requests/no_external_http_requests

Or could we make simple be the default and only require calling a method when the test makes http requests? That would avoid the no_* names above....

[jtgeibel]

I renamed simple to init and full to with_proxy. I rebased to fix merge conflicts and updated the tests converted in the other PR. There are now 50 tests using init and 3 using with_proxy.

bors: r+

[bors-voyager]

Build succeeded

• continuous-integration/travis-ci/push