Use another `execute` wrapper + tiny fixes

* Ditch oslo's `execute` wrapper from utils.py;
* Fix first partition beginning;
* Use proper arguments order for `mdadm`;
* Fix unicode string handling for fs_utils;
* Add sleep to execute;
* Fix nailgun image data fields;

Partially implements: blueprint image-based-provisioning
Change-Id: I2987d4ac0480af48fcccc36a562ac7898e941dc7
Fix fuel_agent, add ceph things

Change-Id: Id23033a537b150875e452f81bd52d63f6286fa1d
Initial Functional Tests for Fuel Agent

Add functional tests for fuel_agent;
Fix simple_http_driver in fuel_agent_ci;
Fix ssh object in fuel_agent_ci;
Fix enviroment object missing imports;

Partially implements: blueprint image-based-provisioning
Change-Id: Ic6739ff9c20547c5d9ab2b4fe9dec45bd5742db9