Revert "ci: temporary metal3 integration job disable"

This reverts commit bd69ef1c57
which was a temporary change in order to facilitate the switch-over
from using eventlet to using threading.

Change-Id: I41efb4ed7c63d67fc1f709055727e624717c91eb
Signed-off-by: Julia Kreger <juliaashleykreger@gmail.com>

zuul.d/project.yaml

@@ -60,11 +60,7 @@
         # NOTE(TheJulia): At present, metal3 doesn't leverage
         # stable branches, and as far as we are aware these jobs
         # can be removed once this branch is made stable.
-        # NOTE(TheJulia): Disabling the Metal3 integration job to allow
-        # us a window to merge the evenetlet removal and related fixes
-        # to make the metal3 integration job generally happy.
-        - metal3-integration:
-            voting: false
+        - metal3-integration
         # Non-voting jobs
         - ironic-inspector-tempest:
             voting: false
@@ -111,7 +107,7 @@
         # NOTE(TheJulia): At present, metal3 doesn't leverage
         # stable branches, and as far as we are aware these jobs
         # can be removed once this branch is made stable.
-        # - metal3-integration
+        - metal3-integration
     experimental:
       jobs:
         # NOTE(dtantsur): this job is rarely used, no need to run it always.