vdsm-tool: speedup loading seboolsetup.py

On RHEL6 "import seobject" takes a very long time. This patch moves the
seobject import statement in seboolsetup.py from module top level to
function level. This small modification reduces the total startup time
of VDSM, since VDSM moves most of the management utilities into
vdsm-tool.

Change-Id: I7f961e2661159f671b17f3ab4fb3d5a7cbc3d6b9
Signed-off-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/16560
Reviewed-by: Dan Kenigsberg <danken@redhat.com>