plugin/tls: respect the path specified by root plugin (#5944)

Signed-off-by: Marius Kimmina <mar.kimmina@gmail.com>

plugin/grpc/setup.go

@@ -3,6 +3,7 @@ package grpc
 import (
 	"crypto/tls"
 	"fmt"
+	"path/filepath"
 
 	"github.com/coredns/caddy"
 	"github.com/coredns/coredns/core/dnsserver"
@@ -110,7 +111,11 @@ func parseBlock(c *caddy.Controller, g *GRPC) error {
 		if len(args) > 3 {
 			return c.ArgErr()
 		}
-
+		for i := range args {
+			if !filepath.IsAbs(args[i]) && dnsserver.GetConfig(c).Root != "" {
+				args[i] = filepath.Join(dnsserver.GetConfig(c).Root, args[i])
+			}
+		}
 		tlsConfig, err := pkgtls.NewTLSConfigFromArgs(args...)
 		if err != nil {
 			return err