validate if timkey is less than equal 0

[ganmacs]

Signed-off-by: Yuta Iwama ganmacs@gmail.com

Which issue(s) this PR fixes:
Fixes #2607

What this PR does / why we need it:

I made a change to raise an error when a user specifies timekey less than equal 0.
when timekey is 0, fluentd will raise ZeroDivisionError at here.

Docs Changes:

no need

Release Note:

same as the title

[repeatedly]

Looks good.

The potential problem is fluentd uses non-strict conversion for parameters like

fluentd/lib/fluent/config/types.rb

Line 101 in 07d9eec

INTEGER_TYPE = Proc.new { |val, opts| val.to_i }

We should improve this point to use Integer() or others.
This change has compatibility probolem so it will be implemented in v2 or via configuration.

[repeatedly]

After test passed, please merge!