unit test for #2815, as requested by @brendandburns
fixed minor formatting
Add an e2e test for exec liveness probes.  Fix the docker exec integration.
Make the test for the 'docker_opts' grain more robust.

Fixes #2982
Merge pull request #2978 from brendandburns/exec

Add an e2e test for exec liveness probes.  Fix the docker exec integration
Merge pull request #2986 from jbeda/docker-default-fix

Make the test for the 'docker_opts' grain more robust.
Merge pull request #2831 from jdef/unit_test_for_2815

unit test for #2815, as requested by @brendandburns