Add fencing agent script as a separated task

Based on nailgun agent, should be installed the same way

Implements blueprint: fencing-in-nailgun-agent

Change-Id: Iceee47c47d35969f4ff08a0eb5b1e74b12b8b92f
Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>