trivial: Use os.uname to get kernel version insteaf of reading proc files

Change-Id: I0bcb4326d6ce4a41486352e11683c83879b61887
Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/12874
Reviewed-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Reviewed-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>