[sheepdog] Jenkins for sheepdog project

[Kai Zhang]

Hi all

I'm very happy to announce that a public Jenkins server for sheepdog has been set up.
Both server and hostname are sponsored by zelin.io

Please check http://jenkins.sheepdog-project.org for more.

Currently, there are only 2 jobs. 
One is for daily build. The other is for testing with local driver. (This is a downstream job of former one)

However, it is still far from enough.
The fowling things will be done soon:
- add github hook so that each commit will trigger a new build
- generate graphical testing report
- add jobs for testing zookeeper and corosync
- fix testing errors

For security reason, only login user can configure jobs and sign up has been disabled.
It would be very appreciated if you would like to contribute on Jenkins. And I will create an account for you.

Thanks,
Kyle