[fuel-plugin] Employ dedicated reboot task

* Use native reboot task after kernel setup to avoid unexpected behavior.
* Add support for removing installed kernel (get back to original one).
* Create symlink to the headers to enable dkms modules
  to get source files of the kernel.

Change-Id: Icdf8db267c69a55337910bc3aed15d56eb783ae5
Signed-off-by: Michael Polenchuk <mpolenchuk@mirantis.com>