Improve task/timer agents execution (see comments)

[oleksandr]

Introduce timeout for a badly written agent program:

package main

import (
    "fmt"
    "os/exec"
    "time"
)

func main() {
    // start
    cmd := exec.Command("sleep", "5")
    if err := cmd.Start(); err != nil {
        panic(err)
    }

    // wait or timeout
    donec := make(chan error, 1)
    go func() {
        donec <- cmd.Wait()
    }()
    select {
    case <-time.After(3 * time.Second):
        cmd.Process.Kill()
        fmt.Println("timeout")
    case <-donec:
        fmt.Println("done")
    }
}