Append .log to file writer filenames

Use a .log suffix for filenames generated by the file writer.

Improve error handling in the CLI.
Rebalancing tests
Updating cartridge versions
Merge pull request #4906 from ironcladlou/logshifter/filenames

Merged by openshift-bot
Merge pull request #4910 from jhadvig/latest_versions_master

Merged by openshift-bot
Merge pull request #4908 from danmcp/master

Merged by openshift-bot
Merge remote-tracking branch 'redhat/master' into master-uhuru

Change-Id: I7e5e893ea092b6ef8c42e48c22f8ff92da9124c9