Updated file store tests to use Dir.mktmpdir to generate random file
store directory names - that fixes intermittent Travis CI build issues
caused by several test suites running in parallel. Temporary files and
directories are now cleaned up in the teardown method.
Merge pull request #579 from bkon/feature/build-temporary-file-racing-condition

Fix for the intermittent CI build failures.
Merge branch 'master' into resolve-mime-type
Avoid testing private apis
Merge branch 'master' into resolve-mime-type