fix(inputs/kube_inventory): don't skip resources with zero s/ns timestamps

[slai]

The previous k8s client library returned times as a generated Time struct that specified time in Seconds and Nanos (https://github.com/ericchiang/k8s/blob/master/apis/meta/v1/generated.pb.go#L1718). Presumably sometimes the API returns pods that were created at the beginning of time or were missing creation timestamps, which should be ignored -

	if p.Metadata.CreationTimestamp.GetSeconds() == 0 && p.Metadata.CreationTimestamp.GetNanos() == 0 {
		return nil
	}

https://github.com/influxdata/telegraf/pull/5110/files#diff-45d12681bfc2ede2a3349288a555ba38819744b3cb829cd131ad8d2b230ce8dbR26

During the switch over to the k8s/client-go library, this logic was retained and rewritten to -

	if p.GetCreationTimestamp().Second() == 0 && p.GetCreationTimestamp().Nanosecond() == 0 {
		return
	}

79f5803#diff-45d12681bfc2ede2a3349288a555ba38819744b3cb829cd131ad8d2b230ce8dbR23

However, in k8s/client-go, times are returned as standard go time.Time structs (with a minor wrapper). Therefore checking whether t.Second() == 0 and t.Nanosecond() == 0 actually only checks whether the second and nanosecond components of time.Time are 0, and not whether the entire timestamp is zero (i.e. not checking day, month, year, hour, minute).

As a result, any pods that were created right at the start of a minute, e.g. 2021-10-22T09:05:00.000Z, are currently being dropped.

This PR fixes that by using the time.IsZero() method instead, and also tweaks the test to check for this scenario.

UPDATE: also applied this fix to the other affected k8s resources.

[telegraf-tiger]

⚠️ This pull request increases the Telegraf binary size by 3.83 % for linux amd64 (new size: 132.1 MB, nightly size 127.2 MB)

📦 Looks like new artifacts were built from this PR.

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Artifact URLs

DEB	RPM	TAR GZ	ZIP
amd64.deb	aarch64.rpm	darwin_amd64.tar.gz	windows_amd64.zip
arm64.deb	armel.rpm	freebsd_amd64.tar.gz	windows_i386.zip
armel.deb	armv6hl.rpm	freebsd_armv7.tar.gz
armhf.deb	i386.rpm	freebsd_i386.tar.gz
i386.deb	ppc64le.rpm	linux_amd64.tar.gz
mips.deb	s390x.rpm	linux_arm64.tar.gz
mipsel.deb	x86_64.rpm	linux_armel.tar.gz
ppc64el.deb		linux_armhf.tar.gz
s390x.deb		linux_i386.tar.gz
		linux_mips.tar.gz
		linux_mipsel.tar.gz
		linux_ppc64le.tar.gz
		linux_s390x.tar.gz
		static_linux_amd64.tar.gz

[powersj]

Thanks for caching this and detailing the issue!