Added LimitNOFILE option in systemd configuration

[SimonBackx]

For servers it's important to have an option to set the maximum open files. Simply adding this in /etc/security/limits.conf won't work because systemd ignores this file. Systemd has an option to set LimitNOFILE in the configuration file, so I added this option.

-- end pull info --

I also tried to solve the systemd spaces in paths issues (#63 , #90 ). I tried using the systemd-escape command (instead of the cmd, cmdEscape template functions). But this didn't worked. Seems like they did change the space handing between different versions of systemd.

service_linux.go:

var tf = map[string]interface{}{
	"cmd": func(s string) string {
		return `"` + strings.Replace(s, `"`, `\"`, -1) + `"`
	},
	"cmdEscape": func(s string) string {
		return strings.Replace(s, " ", `\x20`, -1)
	},
	"systemdEscape": func(s string) string {
		// run systemd-escape command to escape paths properly
		// if something goes wrong we'll default to the original string
		cmd := exec.Command("systemd-escape", "--path", s)

		// Connect pipe to read stdout
		stdout, err := cmd.StdoutPipe()

		if err != nil {
			// Failed to connect pipe
			return s
		}

		// Do not use cmd.Run()
		if err := cmd.Start(); err != nil {
			// Problem while copying stdin, stdout, or stderr
			return s
		}

		slurp, _ := ioutil.ReadAll(stdout)

		if err := cmd.Wait(); err != nil {
			// Command didn't exit with a zero exit status.
			return s
		}

		return string(slurp)
	},
}

However, I did found a solution for #90

service_systemd_linux.go (line 165)

ExecStart=/usr/bin/env "{{.Path}}"{{range .Arguments}} {{.|cmd}}{{end}}

Setting the ExecStart option that way should solve the problem, but this needs more testing.
More info: systemd/systemd#2132