Don't use timekey.object_id for Metadata instance comparison on Windows. Fix #2713

[cosmo0920]

Because this data will be differed unexpectedly on Windows.
This unexpected differing caused flood of buffer files
due to wrong metadata comparision.
hash method inside Metadata struct should be used on non-Windows environment.

This object_id value's unstability is monitored as follows:

{:timekey_object_id=>36247560}
{:timekey_object_id=>36247560}
{:timekey_object_id=>38199640}
{:timekey_object_id=>38199640}
{:timekey_object_id=>38199640}
{:timekey_object_id=>38240520}
{:timekey_object_id=>38240520}
{:timekey_object_id=>38240520}
{:timekey_object_id=>38277560}
{:timekey_object_id=>38277560}
{:timekey_object_id=>38277560}
{:timekey_object_id=>38314220}
{:timekey_object_id=>38314220}
{:timekey_object_id=>38314220}
{:timekey_object_id=>40539060}
{:timekey_object_id=>40539060}
{:timekey_object_id=>40539060}
{:timekey_object_id=>40598620}
{:timekey_object_id=>40598620}
{:timekey_object_id=>40598620}
{:timekey_object_id=>40764680}
{:timekey_object_id=>40764680}
{:timekey_object_id=>40764680}
{:timekey_object_id=>40613600}
{:timekey_object_id=>40613600}
{:timekey_object_id=>40613600}
{:timekey_object_id=>40741660}
{:timekey_object_id=>40741660}
{:timekey_object_id=>40741660}
{:timekey_object_id=>40895360}
{:timekey_object_id=>40895360}
{:timekey_object_id=>40895360}
{:timekey_object_id=>40926520}
<snip>

Signed-off-by: Hiroshi Hatake [email protected]

Which issue(s) this PR fixes:
Fixes #2713

What this PR does / why we need it:
Prevent flood of buffer files which cause BufferOverflowError due to fd limit on Windows.

Docs Changes:
No need.

Release Note:
Same as title.

[ganmacs]

Thank you!!!