virtinst:change default disk bus type into scsi on pseries machine

When install OS from cdrom ,the default cdrom disk bus type is "ide",
which is not supported on pseries machine.But there is no interface to
change it through the whole install process.So we should set "scsi"
(pseries machine support) as default disk type on pseries machine.

Signed-off-by: Qing Lin <qinglbj@linux.vnet.ibm.com>
Signed-off-by: Li Zhang <zhlcindy@linux.vnet.ibm.com>

(crobinso: Add Lin to AUTHORS)

Author: Qing Lin

AUTHORS

@@ -63,6 +63,7 @@ Patches also received from
     Eiichi Tsukata <devel-at-etsukata-dot-com>
     Gaudenz Steinlin <gaudenz-at-debian-dot-org>
     Guannan Ren <gren-at-redhat-dot-com>
+    Qing Lin <qinglbj-at-linux-dot-vnet-dot-ibm-dot-com>
 
     ...send patches and get your name here...
 

virtinst/Guest.py

@@ -1503,7 +1503,11 @@ def _set_defaults(self, devlist_func, remove_func, features):
                     disk.bus = "fdc"
                 else:
                     if self.installer.is_hvm():
-                        disk.bus = "ide"
+                        if (self.installer.type == "kvm" and
+                            self.installer.machine == "pseries"):
+                            disk.bus = "scsi"
+                        else:
+                            disk.bus = "ide"
                     elif self.installer.is_xenpv():
                         disk.bus = "xen"
             used_targets.append(disk.generate_target(used_targets))