Fix time argument formatting to include time zone

[kamalmarhubi]

In local testing, I saw that Container.logs misbehaved when passing the since parameter. I believe this is because my time zone is UTC-4, and so asking for something like

container.logs(since=container.state.started_at)

would return no logs as it was effectively asking for logs from the future:

• container.state.started_at parses the inspect output into a zone-aware datetime; the timezone in inspect's output is always UTC (Z)
• the time formatting in format_time_for_docker strips the time zone rather than converts to local time
• the docker CLI treats its --since argument as being in local time

I instrumented the Popen call to see what arguments were passed to the docker CLI. Taking the exact same command and appending a Z to the time to force the correct time zone printed logs as expected.

[gabrieldemarmiesse]

Many thanks for the thorough bug hunting! That's awesome! From what you described, it sounds like a good fix. I'll take a look in details and give you a review in the next few days :) I also wonder if this kind of bug can occur somewhere else in the codebase.

[kamalmarhubi]

@gabrieldemarmiesse yup I removed my monkey patch to test with current master and it works, thanks!