spec: requires selinux-policy to avoid selinux failure on access tls cert

selinux-policy tightened up the security on svirt_t on fedora18. It causes
that svirt_t is disallowed to access cert_t file. And therefore it will block
qemu run spice server with tls. For more details, please see:
https://bugzilla.redhat.com/show_bug.cgi?id=890345

Change-Id: I9fe74c6187e7e9f2a8c0b2a824d2871fb5497d86
Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/11290
Reviewed-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>