Add e2e test to test docker build failure when the registry is down

[kmala]

ref #deis/dockerbuilder#54

[bacongobbler]

is there someone tackling this or can we punt to post-2.0?

[vdice]

ping @kmala and @mboersma re @bacongobbler's inquiry above ^^

[mboersma]

Punted, although I would like to see this implemented before the v2.0 release. 🏈

[Cryptophobia]

This issue was moved to teamhephy/workflow-e2e#11