func (h DefaultConfigProvider) NewHostSourcer(sourcerType, args string, version int) (dhcplb.DHCPServerSourcer, error) {
	return nil, nil
}
NewHostSourcer returns a dhcplb.DHCPServerSourcer interface.
The default config loader is able to instantiate a FileSourcer by itself, so
NewHostSourcer here will simply return (nil, nil).
The FileSourcer implemments dhcplb.DHCPServerSourcer interface.
If you are writing your own implementation of dhcplb you could write your
custom sourcer implementation here.
sourcerType
The NewHostSourcer function is passed values from the host_sourcer json
config option with the sourcerType being the part of the string before
the : and args the remaining portion.
ex: file:hosts-v4.txt,hosts-v4-rc.txt in the json config file will have
sourcerType="file" and args="hosts-v4.txt,hosts-v4-rc.txt".
package main
import (
	"encoding/json"
	"github.com/facebookincubator/dhcplb/lib"
)
type DefaultConfigProvider struct{}
func NewDefaultConfigProvider() *DefaultConfigProvider {
	return &DefaultConfigProvider{}
}