Switch to quay.io for E2E test image to avoid throttling

[jgwest]

What does this PR do / why we need it:

• Some of our E2E tests use a docker.io-hosted image with a generic tag, which means we are subject to docker.io rate limiting (causing E2E tests to fail), and the contents of the image may change arbitrarily
• I've mirrored the image to quay.io to avoid rate limiting on image pulls, and hardcoded the SHA in the test to ensure the content doesn't change
• There's probably an even better place for it, or an alternative image, but for this PR the perfect is the enemy of the good

[chetan-rns]

/lgtm

We should consider migrating to the official argoprojlabs repo https://quay.io/organization/argoprojlabs

[jgwest]

Thanks @chetan-rns , I have opened #67 to track the migration.