lib/oe/utils: Improve multiprocess_lauch exception handling

We've seen a cryptic:

"ERROR: Fatal errors occurred in subprocesses, tracebacks printed above"

message from oe-selftest with no other traceback information. Improve the
traceback logging to try and give a better indication of any errors that is
ocurring.

(From OE-Core rev: 521dd3d00979a27b6932e58d5497de68abac26e1)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oe/utils.py

@@ -318,9 +318,10 @@ def multiprocess_launch(target, items, d, extraargs=None):
     for p in launched:
         p.join()
     if errors:
+        msg = ""
         for (e, tb) in errors:
-            bb.error(str(tb))
-        bb.fatal("Fatal errors occurred in subprocesses, tracebacks printed above")
+            msg = msg + str(e) + ": " + str(tb) + "\n"
+        bb.fatal("Fatal errors occurred in subprocesses:\n%s" % msg)
     return results
 
 def squashspaces(string):

meta/lib/oeqa/selftest/cases/oelib/utils.py

@@ -66,6 +66,9 @@ class TestMultiprocessLaunch(TestCase):
 
         def dummyerror(msg):
             print("ERROR: %s" % msg)
+        def dummyfatal(msg):
+            print("ERROR: %s" % msg)
+            raise bb.BBHandledException()
 
         @contextmanager
         def captured_output():
@@ -79,6 +82,7 @@ class TestMultiprocessLaunch(TestCase):
 
         d = bb.data_smart.DataSmart()
         bb.error = dummyerror
+        bb.fatal = dummyfatal
 
         # Assert the function returns the right results
         result = multiprocess_launch(testfunction, ["3", "4", "5", "6"], d, extraargs=(d,))