generic.tests.cfg: Update kdump config

kdump test should be linux guest only, so disable windows guest.
Signed-off-by: NShuping Cui <scui@redhat.com>

generic/tests/cfg/kdump.cfg

 - kdump: install setup image_copy unattended_install.cdrom
     virt_test_type = qemu libvirt
-    only RHEL.5, RHEL.6
+    no Windows
+    no RHEL.3, RHEL.4
     type = kdump
     # time waited for the completion of crash dump
     crash_timeout = 1200