Fix out_file test with timezone

[repeatedly]

@mururu Could you test this on your environment?

In v0.14, compat parameters handles utc parameter for parsers / formatters.
So if we want to use utc in buffer, need to specify timekey_use_utc in <buffer>.

[mururu]

Passed tests on my environment.
IIRC, v0.14 should work with v0.12's output configuration parameters? If so, we should fix the implementation of the compatibility layer but not tests? Otherwise, it looks good to me.

[repeatedly]

If so, we should fix the implementation of the compatibility layer but not tests?

Yeah, this is one idea. The problem is old out_file uses utc for both time slice and formatter.
In this result, hard to identify this parameter is for output or formatter.
We want to resolve this problem with v0.14.
Other idea is logging warning message like below.

'utc' parameter for output is deprecated and this parameter is used for formatter plugin. Use timekey_use_utc in <buffer> instead

[mururu]

That makes sense.
Another concern is that if a user explicitly set time_slice_format in addition to utc, then <buffer> timekey_use_utc true </buffer> is inserted automatically, right? It is confusing for me. Is it no problem?

[repeatedly]

then timekey_use_utc true is inserted automatically, right?

Yes. Maybe keeping existing behaviour is not good for both developers and users.
So this seems decision and documentation issue.
Currently, no report from users for out_file.
So earlier is better for it.

[repeatedly]

Add warning message.

[mururu]

Makes sense. LGTM.