more robust resolv.conf check

[wjayesh]

As the comment below mentions, in order to check the resolv.conf for different namespaces, we have to look into the /etc/namespace/../ dir for that version of resolv.conf.

coredns-healthcheck/pkg/engine/engine.go

Lines 175 to 177 in 468a6f2

	// check if etc/namespace exists or not
	// this is because we can't access it directly as setns doesn't
	// relocate etc/namespace/.../ to etc/resolv.conf

Currently only the one that version of resolv.conf is checked that is shared across all network namespaces. Those net ns that have their own versions are not checked.

coredns-healthcheck/pkg/netns/remedy.go

Lines 24 to 27 in 468a6f2

	//first, we check the resolv.conf file to check if resolvers are correct
	//
	cmd := exec.Command("cat", "/etc/resolv.conf")
	output, err := cmd.CombinedOutput()

We can do that in the remedy.go file, keeping in mind that we already have the namespace information (as a netns object).