Make sure there is no automatic GC happening concurrently

It is not safe to run multiple JGit GC at the same time.
Make sure that there is no automatic GC happening on the repo
prior to start a JGit GC activity.

Change-Id: I7bc6b258ed469050bda9d2fdda99ebe00fdb7de5
diff --git a/maintenance/git-gc/scripts/utils.sh b/maintenance/git-gc/scripts/utils.sh
index 8ce4bb6..1213c7e 100755
--- a/maintenance/git-gc/scripts/utils.sh
+++ b/maintenance/git-gc/scripts/utils.sh
@@ -52,6 +52,10 @@
       return 1
     }
 
+    log_project "$proj" "Disable JGit automatic GC (gc.auto=0; gc.autoPackLimit=0)"
+    $GIT config gc.auto 0
+    $GIT config gc.autoPackLimit 0
+
     if should_create_bitmaps "$proj"
     then
       $GIT config pack.buildBitmaps true