buildman: Enable test coverage

Enable measuring test coverage for buildman so we can see the gaps. It is
currently at 68%.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/buildman/cmdline.py b/tools/buildman/cmdline.py
index 052e223..03211bd 100644
--- a/tools/buildman/cmdline.py
+++ b/tools/buildman/cmdline.py
@@ -142,6 +142,8 @@
                           help='Skip tests which need the network')
         parser.add_argument('-t', '--test', action='store_true', dest='test',
                           default=False, help='run tests')
+        parser.add_argument('--coverage', action='store_true',
+                            help='Calculated test coverage')
     parser.add_argument('-T', '--threads', type=int,
           default=None,
           help='Number of builder threads to use (0=single-thread)')