Add post deployment tests for main branch staging deploys

[halkyon]

This is the second part of https://github.com/storj/gateway-mt/issues/57 in which we run some tests to make sure the build that just got deployed to staging is working as expected.

We could use some of the existing testsuite scripts. I would say it doesn't have to test every last thing, but enough as a smoke test to make sure the environment works as expected.