Link to the tail of the console log, instead of the full log. That's
bound to have the info the user is looking for, and at the same time
loads way more quickly than the (huge) full log, which is just one click
away if needed.

Author: Marcelo Vanzin <vanzin@cloudera.com>

Closes #6664 from vanzin/jenkins-link and squashes the following commits:

ba07ed8 [Marcelo Vanzin] [minor] [build] Change link to jenkins builds on github.