Add TXT record with container ID length 60 to keep logical process in the script

[x3rus]

Hi,
So here the patch suggestion , of course it's include my 2 other pull request .
To fix the issues , I keep the idea of the script , I fix the update template to add container ID .

Maybe I will use the script on many docker host , so short container id with length 12 is a little bit scary , but we can't use full length because the maximum length is 63 , that's why I use 60 :D .

Now I'm able to pull TXT record with the container id , example

$ docker run -it --name fixDns --hostname fixUpadte  ubuntu:14.04 bash

$ dig fixDns.dck.example.com
;; ANSWER SECTION:
fixDns.dck.example.com.   600     IN      CNAME   fixUpadte.dck.example.com.
fixUpadte.dck.example.com. 60     IN      A       172.17.0.4

$ dig TXT 3d27aaa9095cfa617d0d7f0c53f9d853b5f9df68d2914405e6f0e003ada0.dck.example.com
;; ANSWER SECTION:
3d27aaa9095cfa617d0d7f0c53f9d853b5f9df68d2914405e6f0e003ada0.dck.example.com. 600 IN TXT "dockerDDNS-alias:fixDns:"

This patch don't fix issue #13 , I steel have a small issue the CNAME and the TXT record for the container but the A record is steel there. I will work on it soon.

Thanks for your work BTW , I learn so much