Use formal error checking to validate a not found err.
add coreos setup guides
Merge pull request #1576 from kelseyhightower/add-coreos-docs

add coreos setup guides
Merge pull request #1577 from brendandburns/fix

Use formal error checking to validate a not found err.
Fix integration test read volume dir error.
Merge pull request #1579 from ddysher/integration-fix

Fix integration test read volume dir error.