Change to using gopsutil for cross-OS process ops

Instead of trying to write out own code to do basic process
operations (e.g. checking if a PID is still running in a multi-OS
friendly manner), use shirou/gopsutil, a multi-platform library
that should abstract all the complexity away. Unlike our previous
approach on Windows, this one should actually work.

Signed-off-by: Matt Heon <mheon@redhat.com>

vendor/github.com/tklauser/go-sysconf/sysconf_bsd.go

@@ -0,0 +1,38 @@
+// Copyright 2018 Tobias Klauser. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build darwin || dragonfly || freebsd || netbsd || openbsd
+// +build darwin dragonfly freebsd netbsd openbsd
+
+package sysconf
+
+import "golang.org/x/sys/unix"
+
+func pathconf(path string, name int) int64 {
+	if val, err := unix.Pathconf(path, name); err == nil {
+		return int64(val)
+	}
+	return -1
+}
+
+func sysctl32(name string) int64 {
+	if val, err := unix.SysctlUint32(name); err == nil {
+		return int64(val)
+	}
+	return -1
+}
+
+func sysctl64(name string) int64 {
+	if val, err := unix.SysctlUint64(name); err == nil {
+		return int64(val)
+	}
+	return -1
+}
+
+func yesno(val int64) int64 {
+	if val == 0 {
+		return -1
+	}
+	return val
+}