Add print task.

Made a task that simply prints the output that is given to it as
an argument. Can be used like any other task (under sequential,
etc...)

IE:

tasks:
- print: "String"
- chef: null
- print: "Another String"

Signed-off-by: Sandon Van Ness <sandon@inktank.com>
Signed-off-by: Yuri Weinstein <yuri.weinstein@inktank.com>
Merge pull request #220 from ceph/wip-print

Add print task.