Switch to own exception.

Instead of raising ValueError, which is used all the time, except
DisconnectedSoftwareTree exception.

It allows to have selective detection of software instance problem and allows
to test what exactly was told.

master/product/Vifib/tests/testVifibSlapWebService.py

@@ -8049,12 +8049,13 @@ class TestVifibSlapWebService(testVifibMixin):
     sequence_list.addSequenceString(sequence_string)
     sequence_list.play(self)
 
-  def stepDirectRequestComputerPartitionRaisesValueError(self,
+  def stepDirectRequestComputerPartitionRaisesDisconnectedSoftwareTree(self,
     sequence, **kw):
     software_instance = self.portal.portal_catalog.getResultValue(
       uid = sequence['software_instance_uid'])
     requested_reference = sequence['requested_reference']
-    self.assertRaises(ValueError,
+    from erp5.document.SoftwareInstance import DisconnectedSoftwareTree
+    self.assertRaises(DisconnectedSoftwareTree,
       software_instance.requestSoftwareInstance,
       software_release=sequence['software_release_uri'],
       software_type=sequence['requested_reference'],
@@ -8193,7 +8194,7 @@ class TestVifibSlapWebService(testVifibMixin):
       SelectRequestedReferenceB
 
       LoginDefaultUser # login as superuser in order to work in erp5
-      DirectRequestComputerPartitionRaisesValueError
+      DirectRequestComputerPartitionRaisesDisconnectedSoftwareTree
       """
     sequence_list.addSequenceString(sequence_string)
     sequence_list.play(self)