get_binary_name should returns strings without spaces

get_binary_name should returns strings without spaces

Iptables does not support chain names with spaces. It implies
get_binary_name should return strings without spaces (they are used as
chain name prefix). But currently 'python -m unittest $module' implies
spaces in get_binary_name() result, it disallows to use it when $module
is a functional test module. This change replaces spaces with
underscores in get_binary_name results.

Change-Id: Ie7c8518b92be46a4eea4e9345713fdeba844126d
Closes-Bug: #1404250