func NewAuthConfigurationsFromFile(path string) (*AuthConfigurations, error) {
	r, err := os.Open(path)
	if err != nil {
		return nil, err
	}
	return NewAuthConfigurations(r)
}
NewAuthConfigurationsFromFile returns AuthConfigurations from a path containing JSON
in the same format as the .dockercfg file.
package docker
import (
	"bytes"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path"
	"strings"
)
var ErrCannotParseDockercfg = errors.New("Failed to read authentication from dockercfg")
type AuthConfiguration struct {
	Username      string `json:"username,omitempty"`
	Password      string `json:"password,omitempty"`
	Email         string `json:"email,omitempty"`
	ServerAddress string `json:"serveraddress,omitempty"`
}
type AuthConfigurations struct {
	Configs map[string]AuthConfiguration `json:"configs"`
}
type AuthConfigurations119 map[string]AuthConfiguration
type dockerConfig struct {
	Auth  string `json:"auth"`
	Email string `json:"email"`
}