test(ci): report results to CircleCI via JUnit

[zetlen]

This PR is a:

[ ] New feature
[ ] Enhancement/Optimization
[ ] Refactor
[ ] Bugfix
[x] Test for existing code
[ ] Documentation

Summary

When this pull request is merged, it will adjust CI and DangerCI setup to

• always run tests, even on non-PR branches that don't run Danger
• reuse test results in Danger analysis
• output and store test results in CircleCI for better analysis purposes

[coveralls]

Pull Request Test Coverage Report for Build 548

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 462 unchanged lines in 35 files lost coverage.
• Overall coverage decreased (-26.4%) to 30.46%

---

Files with Coverage Reduction	New Missed Lines	%
packages/venia-concept/src/shared/images.js	1	0.0%
packages/venia-concept/src/util/timeout.js	1	0.0%
packages/peregrine/src/store/middleware/log.js	1	0.0%
packages/peregrine/src/store/middleware/index.js	2	0.0%
packages/peregrine/src/util/unaryMemoize.js	3	0.0%
packages/venia-concept/src/util/initObserver.js	4	0.0%
packages/venia-concept/src/util/fixedObserver.js	4	0.0%
packages/venia-concept/src/components/Button/button.js	4	0.0%
packages/venia-concept/src/classify.js	4	0.0%
packages/peregrine/src/store/index.js	5	0.0%

Totals
Change from base Build 525:	-26.4%
Covered Lines:	519
Relevant Lines:	1709

---

💛 - Coveralls

[zetlen]

I'm 😱 unilaterally 😱 merging this, because our broken tests are making it hard to evaluate other PRs for stability, and it's blocking everyone.