Correct exception args in vfs/guestfs.

Updates the exception formatting in vfs/guestfs so that we
properly raise in cases where there is no root or multiple
roots.

Fixes a TypeError that would occur with the previous code.

Fixes LP Bug #1153414.

Change-Id: I28f9cde5a2da466ebb7397176baaf051ccd4192b

nova/tests/test_virt_disk_vfs_guestfs.py

@@ -16,6 +16,7 @@
 
 import sys
 
+from nova import exception
 from nova import test
 
 from nova.tests import fakeguestfs
@@ -51,6 +52,32 @@ class VirtDiskVFSGuestFSTest(test.TestCase):
         self.assertEqual(handle.closed, True)
         self.assertEqual(len(handle.mounts), 0)
 
+    def test_appliance_setup_inspect_no_root_raises(self):
+        vfs = vfsimpl.VFSGuestFS(imgfile="/dummy.qcow2",
+                                 imgfmt="qcow2",
+                                 partition=-1)
+        # call setup to init the handle so we can stub it
+        vfs.setup()
+
+        def fake_inspect_os():
+            return []
+
+        self.stubs.Set(vfs.handle, 'inspect_os', fake_inspect_os)
+        self.assertRaises(exception.NovaException, vfs.setup_os_inspect)
+
+    def test_appliance_setup_inspect_multi_boots_raises(self):
+        vfs = vfsimpl.VFSGuestFS(imgfile="/dummy.qcow2",
+                                 imgfmt="qcow2",
+                                 partition=-1)
+        # call setup to init the handle so we can stub it
+        vfs.setup()
+
+        def fake_inspect_os():
+            return ['fake1', 'fake2']
+
+        self.stubs.Set(vfs.handle, 'inspect_os', fake_inspect_os)
+        self.assertRaises(exception.NovaException, vfs.setup_os_inspect)
+
     def test_appliance_setup_static_nopart(self):
         vfs = vfsimpl.VFSGuestFS(imgfile="/dummy.qcow2",
                                  imgfmt="qcow2",