Fixed missing build requirements for debian

* Added python-ipaddr
* Added python-netifaces
* Added python-configobj
Added python2.7 compatibility for debian

* Also dropped obsolete python 2.5 compatibility
Added convert_bytes_to_human() in utils

* Based on commit c9d26cfb1730189307cd4e818cd4ef2add1f59d0
	Author: Andy Grover <agrover@redhat.com>
	Date:   Tue Dec 13 11:32:50 2011 -0800

	    Rename convert_human_to_bytes(). Add bytes_to_human()

	    x_to_y already connotes conversion, so omit the "convert_" prefix for
	    brevity.

	    Add a corresponding bytes_to_human(), which targetcli uses.

	    Signed-off-by: Andy Grover <agrover@redhat.com>