Merge ~adam-collard/maas:pod-discovery-error into maas:master

[Adam Collard]

PodProblem raised in discovery includes original exception

[Alberto Donato (ack)]

+1

review: Approve

[MAAS Lander (maas-lander)]

UNIT TESTS
-b pod-discovery-error lp:~adam-collard/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: FAILED
LOG: http://maas-ci.internal:8080/job/maas-tester/1009/consoleText
COMMIT: bc7120d951c86776ef72b561b37117a705fd789a

review: Needs Fixing

[MAAS Lander (maas-lander)]

LANDING
-b pod-discovery-error lp:~adam-collard/maas/+git/maas into -b master lp:~maas-committers/maas

STATUS: FAILED BUILD
LOG: http://maas-ci.internal:8080/job/maas-tester/1010/consoleText

diff --git a/src/maasserver/tests/test_vmhost.py b/src/maasserver/tests/test_vmhost.py
index 996e3a1..3db3667 100644
--- a/src/maasserver/tests/test_vmhost.py
+++ b/src/maasserver/tests/test_vmhost.py
@@ -199,6 +199,7 @@ class TestDiscoverAndSyncVMHost(MAASServerTestCase):
             factory.make_User(),
         )
         self.assertEqual(str(exc), str(error))
+        self.assertIs(error.__cause__, exc)
 
 
 class TestDiscoverAndSyncVMHostAsync(MAASTransactionServerTestCase):
@@ -274,6 +275,7 @@ class TestDiscoverAndSyncVMHostAsync(MAASTransactionServerTestCase):
         except Exception as error:
             self.assertIsInstance(error, PodProblem)
             self.assertEqual(str(exc), str(error))
+            self.assertIs(error.__cause__, exc)
         else:
             self.fail("No exception raised")
 
diff --git a/src/maasserver/vmhost.py b/src/maasserver/vmhost.py
index da4e18e..9ee1f73 100644
--- a/src/maasserver/vmhost.py
+++ b/src/maasserver/vmhost.py
@@ -82,7 +82,7 @@ def discover_and_sync_vmhost(vmhost, user):
         )
         discovered_pod = get_best_discovered_result(discovered)
     except Exception as error:
-        raise PodProblem(str(error))
+        raise PodProblem(str(error)) from error
 
     if discovered_pod is None:
         raise PodProblem(
@@ -118,7 +118,7 @@ async def discover_and_sync_vmhost_async(vmhost, user):
         )
         discovered_pod = get_best_discovered_result(discovered)
     except Exception as error:
-        raise PodProblem(str(error))
+        raise PodProblem(str(error)) from error
 
     if discovered_pod is None:
         raise PodProblem(