Pull request: 2231 autoupdate

Merge in DNS/adguard-home from 2231-autoupdate to master

Updates #2231.

Squashed commit of the following:

commit 4ee9148ee7a38f2759898302a2109aa982fb4ee9
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Nov 30 19:08:14 2020 +0300

    sysutil: provide os-independent interface

commit 778097c5fdeb1dec94f4cfc6443d08f92d9db0ba
Author: Eugene Burkov <e.burkov@adguard.com>
Date:   Mon Nov 30 16:40:33 2020 +0300

    all: add sysutil package

internal/sysutil/sysutil.go

@@ -0,0 +1,31 @@
+// Package sysutil contains utilities for functions requiring system calls.
+package sysutil
+
+import "syscall"
+
+// CanBindPrivilegedPorts checks if current process can bind to privileged
+// ports.
+func CanBindPrivilegedPorts() (can bool, err error) {
+	return canBindPrivilegedPorts()
+}
+
+// SetRlimit sets user-specified limit of how many fd's we can use
+// https://github.com/AdguardTeam/AdGuardHome/internal/issues/659.
+func SetRlimit(val uint) {
+	setRlimit(val)
+}
+
+// HaveAdminRights checks if the current user has root (administrator) rights.
+func HaveAdminRights() (bool, error) {
+	return haveAdminRights()
+}
+
+// SendProcessSignal sends signal to a process.
+func SendProcessSignal(pid int, sig syscall.Signal) error {
+	return sendProcessSignal(pid, sig)
+}
+
+// ConfigureSyslog reroutes standard logger output to syslog.
+func ConfigureSyslog(serviceName string) error {
+	return configureSyslog(serviceName)
+}