Allow selection of hypervisor type in QA

This patch allows the selection of the hypervisor type for the QA
process; this is useful when testing hypervisor-independent changes that
don't require a Xen setup.

The patch also fixes the OS name in the sample QA config file provided.

Reviewed-by: imsnah

qa/qa-sample.yaml

 # Cluster name
 name: xen-test
+hypervisor-type: xen-3.0
 
 # System to use
-os: debian-edgy
+os: debian-etch
 os-size: 10G
 swap-size: 1G
 mem: 512M

qa/qa_cluster.py

@@ -66,6 +66,10 @@ def TestClusterInit():
     cmd.append('--bridge=%s' % bridge)
     cmd.append('--master-netdev=%s' % bridge)
 
+  htype = qa_config.get('hypervisor-type', None)
+  if htype:
+    cmd.append('--hypervisor-type=%s' % htype)
+
   cmd.append(qa_config.get('name'))
 
   AssertEqual(StartSSH(master['primary'],