Issue #241: require python-psutil version

commit c8a25fd will blocks some kimchi host monitor on some old distros.
Actually we do not need the new function of pustil.
I have check the psutil code, it just a warning, no harmful.

The new function can be available from 0.6.0 version.
And the 0.6.0 is released on 2012-08-13.
Now we need require python-psutil version.
If on some distros, the python-psutil version is less than 0.6.0,
We require the kimchi user upgrade their python-psutil.

More details as follow.
The psutil features history:
https://psutil.googlecode.com/hg/HISTORY

0.6.0 - 2012-08-13
------------------

NEW FEATURES

 * #311: system memory functions has been refactorized and rewritten and now
         provide a more detailed and consistent representation of the system
         memory. New psutil.virtual_memory() function provides the following
         memory amounts:
          - total
          - available
          - percent
          - used
          - active [POSIX]
          - inactive [POSIX]
          - buffers (BSD, Linux)
          - cached (BSD, OSX)
          - wired (OSX, BSD)
          - shared [FreeBSD]

API CHANGES

 * psutil.phymem_usage() is deprecated             (use psutil.virtual_memory())
 * psutil.virtmem_usage() is deprecated            (use psutil.swap_memory())
 * psutil.phymem_buffers() on Linux is deprecated  (use psutil.virtual_memory())
 * psutil.cached_phymem() on Linux is deprecated   (use psutil.virtual_memory())
 * [Windows and BSD] psutil.virtmem_usage() now returns information about swap
   memory instead of virtual memory.

Signed-off-by: ShaoHe Feng <shaohef@linux.vnet.ibm.com>