Fix sslTests import bug

ImportError for SecureXMLRPCServer is triggered when the test runns in
installed directory.
It should be imported from vdsm folder in python library.

Change-Id: Ia1742e8428dacaf4c56c52e88f29d6fb1625b833
Signed-off-by: MeiLiu <liumbj@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/12467
Reviewed-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Tested-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>