Reset Octokit before and after Authorization and Client specs

Added `Octokit.reset!` calls to before and after in the top level of the
Authorizations and Client specs.

Fixes cases such as https://travis-ci.org/octokit/octokit.rb/jobs/16294010
where the modified client leaked between test cases causing seemingly
random VCR request match failures.

I'm not sure how to run select specs in a certain order so I brute forced
my way to reproducing the issue with the following:

```bash
$ while clear; script/test; do :; done
```